Rate & Sum Finance calculators
Menu

Browse

Categories

Open a calculator

Methodology

How these
numbers are made.

Every calculator here runs on one tested engine, uses the conventions US lenders actually use, and rounds the way a lender rounds. This page states the formulas, names the file each one lives in, and says plainly where a figure is an industry habit rather than a legal rule.

The formulas

One engine, shared by every loan and mortgage tool on the site. Written once so a fix reaches all of them, and tested once so it has to.

The payment on a fully amortising loan is the standard annuity formula. It lives in src/lib/engine/core.ts and is the same expression in the code as it is here: 

PMT = P × i / (1 − (1 + i)^−n)

P = principal (the amount borrowed)
i = periodic interest rate, as a decimal
n = total number of payments

At a zero interest rate that expression divides by zero, so the engine takes a separate branch and returns P / n — the honest answer for an interest-free loan, and a case real tools get wrong by returning NaN. Payments are returned unrounded from this function so that the caller decides where rounding happens, which matters more than it sounds; see the rounding section below.

The periodic rate comes from the annual rate by simple division: 

i = (annual rate ÷ 100) ÷ payments per year

This is a convention, not a law of arithmetic. Dividing a nominal annual rate by the number of periods is what US lenders and every mainstream calculator do, so following it is what makes our figures match your loan statement. It is not the same as the effective-rate conversion (1 + r)^(1/n) − 1, which would give a slightly different number. The engine implements both and keeps them separate: the second is used only where an effective annual rate is genuinely what is being reported, such as APY.

Rounding, and why the total is a few cents off

The schedules here round the way a lender rounds, which is not the way a spreadsheet formula rounds.

A lender quotes a payment rounded to the cent and then charges exactly that amount every period. Interest is computed on the outstanding balance and rounded to the cent; principal is whatever is left of the payment. The engine replicates that sequence rather than carrying full precision through 360 periods.

The consequence is deliberate and worth stating plainly, because a careful reader will otherwise think they have found a bug:

Total interest on our schedules differs by a few cents from the closed-form payment × n − principal. That difference is the correct answer, not an error. The closed-form version assumes a payment with infinite decimal places, which no lender charges.

Rounding itself is half away from zero, not JavaScript's built-in rounding — which rounds half toward positive infinity and so treats −0.5 differently from 0.5. Financial rounding is symmetric about zero, so the engine rounds the magnitude and reapplies the sign. It also nudges by a scaled epsilon before rounding, because values such as 1.005 are stored in binary as 1.00499999999999989… and would otherwise round down where a human expects up. Both behaviours are tested directly, at the .005 boundary and across signs.

The final payment

Because the quoted payment is rounded, it does not divide the balance perfectly. A payment rounded down leaves a shortfall of a few cents each period, and over a 30-year term that accumulates into a spurious 361st payment of a few dollars. Some calculators show exactly that, and it is wrong: a lender runs the contracted term and adjusts the last payment.

So a schedule here holds the payment level and absorbs all accumulated drift into the final one. A 30-year monthly loan produces exactly 360 rows — never 361 — and the closing balance is exactly zero rather than a rounding artefact near zero. Extra payments may still end a loan early; the rule pins the upper bound, not the lower.

Every schedule the engine produces is checked against the same set of structural invariants, whatever the inputs: the balance ends at exactly zero, never rises and never goes negative; each row's interest plus principal reconciles to its payment; the principal repaid sums to the amount borrowed to the cent; and no schedule contains NaN or Infinity anywhere. Those hold across every payment frequency, at zero interest, on a single-payment loan, on a fractional term and on a very large principal.

How the maths is checked

A calculator that agrees only with itself has not been verified. These agree with sources outside their own code.

Expected values in the engine tests are computed independently of the implementation: by hand from the closed-form formula, from published worked examples, or from standard spreadsheet functions — PMT, FV, PV, RATE, IRR — which are the de-facto reference for these formulas. Two examples, quoted from the test file: 

PMT(0.065/12, 360, -420000) = 2654.68569867045
PMT(0.05/12,   60,  -25000) =  471.780841100275

Those are the figures the engine must reproduce, to ten significant figures, before a page using it can ship. The point of sourcing them from a spreadsheet is that a spreadsheet was not written by us: if our formula and our expectation were both derived from the same reasoning, agreement between them would prove nothing.

Alongside the fixed reference values, the suite asserts invariants that must hold for any inputs rather than for one chosen case — the schedule integrity rules in the previous section are checked that way, as is the requirement that paying more often never increases total interest. Edge cases get their own tests: zero interest, a one-payment loan, a fractional term, a principal small enough to round to nothing, a rate so high the loan cannot amortise at all. The last of those must produce a clear explanation rather than a hang or an Infinity.

That is 1599 tests over 51 files covering the engine, the 15 published calculators, the money formatting, the interactive views and the site's own URL structure. All of them run before a build is considered good, and the count on this page is reconciled against the files on disk by one of them.

What automated tests do not cover, stated so the claim above is not read as broader than it is: keyboard-only navigation, screen-reader output, print layout and performance auditing have not yet been run on these pages. Those are manual passes, and this page will say so until they have been done.

Rules, conventions and the difference

Some numbers in lending are law. Most of the famous ones are habit. We label which is which.

A great deal of published financial guidance states industry conventions as though they were requirements. It matters because the two behave differently: a statutory threshold applies whether or not a lender likes it, while a convention varies by lender, by programme and by year, and can be argued with.

Statutory — cited to the primary source

PMI termination is the clearest example. The Homeowners Protection Act sets it, so our mortgage tools model it and link to the statute. Automatic termination at 78% loan-to-value requires only that the borrower be current on payments; the separate request path at 80% carries additional conditions. Fixed-rate loans use the initial amortisation schedule for that test. Where we model a rule like this, the rule is the authority and we cite it.

Convention — labelled every time it appears

The 28/36 debt-to-income rule is the best-known figure in US mortgage guidance and it has no primary source. We looked: it is absent from Fannie Mae's Selling Guide, from the CFPB's debt-to-income material, and from the HUD regulation at 24 CFR 203.33, which contains no percentages at all. So our affordability and debt-to-income tools use it — because lenders do — and name it as a convention on every occasion, including in the input hints beside the fields themselves.

The 43% figure needs its own note, because it is frequently cited as the Qualified Mortgage limit and that is no longer accurate. The rule was amended to replace its DTI ceiling with a price-based test, so 43% survives as a lender habit rather than a legal threshold. Our pages say that rather than repeating the older claim.

The practical test we apply: if we cannot point to a statute or regulation, the number is described as what lenders conventionally do — never as what is required, and never as a prediction of approval. A ratio inside every convention does not make borrowing wise, and one outside them does not make an application hopeless.

Where a claim is measured rather than sourced

Occasionally the honest answer is neither law nor convention but arithmetic that contradicts common advice. "Biweekly payments save thousands in interest" is the standard case. Paying half a monthly payment every two weeks means 26 half-payments a year, which is 13 monthly payments rather than 12 — so almost all of the advertised saving is the extra payment, not the change in frequency. We separate the two effects in the amortisation tool and report them individually, because a reader whose lender will not accept fortnightly billing can capture nearly all of the benefit by adding a twelfth of a payment each month. Figures of that kind are derived from the engine in tests, never restated as prose constants.

Where your figures go

Nowhere, while you type — with one exception we would rather state than have you find.

Every calculation on this site runs in your browser. There is no endpoint that accepts your income, balances, loan amounts or property values, and no record of a calculation is kept — the arithmetic is JavaScript that ships with the page and executes on your device.

That is worth distinguishing from a privacy promise. A site that computed your figures on a server could promise not to keep them, and you would have to take its word. Here there is nothing to keep them in, which is a stronger guarantee than any policy statement because it does not depend on our conduct.

There is one case where the figures do cross the network, and it is a case this site actively encourages. Sharing a result works by putting the inputs in the URL. While you type, that rewrite is local. But when someone opens that link, the query string travels in the request line like any address, so the figures in it reach the server that serves the page — which is the one moment the architecture above does not cover. What we do and do not receive in that case is set out in full on the privacy page.

One further consequence follows honestly. Analytics, where enabled, records that a calculator was used and which one — never the values entered, and never the query string that might contain them.

Sources

Primary law and regulator guidance, each carrying the date it was last checked.

Every source cited by a published calculator, gathered here. This list is generated from the tools themselves rather than maintained separately, so it cannot fall out of step with what the pages actually rely on. A retrieval date is given because regulations are amended: it tells you how current our reading is, and lets you check whether anything has changed since.

  1. 12 CFR § 1026.53 — Allocation of payments The requirement that a card issuer allocate amounts paid above the required minimum payment first to the balance carrying the highest annual percentage rate, then to remaining balances in descending rate order, with exceptions in paragraph (b) for deferred-interest and secured balances. It governs allocation between balances WITHIN one credit card account under an open-end plan that is not home-secured; it says nothing about the order in which a consumer should pay separate debts, and is not an endorsement of either strategy on this page. Checked 2026-09-19
  2. 12 CFR § 1026.7 — Periodic statement (paragraph (b)(12), Repayment disclosures) The requirement that a credit card statement disclose the cost of paying only the minimum and the estimated monthly payment that would repay the balance in 36 months, at paragraph (b)(12)(i)(F)(1)(i). This is the basis for the three-year benchmark row on this page. Note that paragraph (b)(11) is "Due date; late payment costs" and is a different requirement entirely. Checked 2026-09-19
  3. 12 CFR 1026.43(e)(2) — Qualified Mortgage standards The current text of the ability-to-repay rule, which requires a lender to consider and verify debt-to-income or residual income but contains no numeric DTI ceiling — the basis for correcting the widespread claim that 43% is a legal limit. Checked 2026-09-19
  4. 12 CFR 1030.2 — Truth in Savings definitions, including annual percentage yield The regulatory definition of annual percentage yield, which is why a quoted APY is comparable between deposit accounts while a bare interest rate is not. It does not establish any rate level and does not govern investment returns. Checked 2026-09-19
  5. 15 U.S.C. § 1637 — Truth in Lending Act, open-end credit disclosures The statutory basis for the minimum-payment disclosures, at subsection (b)(11). Worth distinguishing from the regulation: the statute requires the 36-month payment and the total cost of paying over 36 months, but does not itself require the savings comparison that appears on statements. That comparison is a Regulation Z addition, not a statutory mandate. Checked 2026-09-19
  6. 17 CFR 230.156 — Investment company sales literature The standard this page applies to its own framing of a past return: sales literature is misleading where it contains an untrue statement of a material fact, and specifically where it makes representations implying that future gains or income may be inferred from or predicted on the basis of past investment performance, or portrays past performance in a manner implying that past gains would be repeated. It governs investment company sales literature rather than calculators, and it establishes none of the arithmetic here. Checked 2026-09-19
  7. 17 CFR 230.482 — Advertising by an investment company The convention this page follows in leading with an annualised figure and stating the past-performance caveat prominently. The rule requires advertisements containing performance data to carry a legend stating that the data represents past performance and that past performance does not guarantee future results, presented in the body of the advertisement and not in a footnote; and it requires average annual total return for one, five and ten year periods, set out with equal prominence and identifying the length and end date of each period. It applies to registered investment company advertising, not to this calculator. Checked 2026-09-19
  8. American Express — Gold Card cardmember agreement, minimum payment clause (as of 30 June 2026) The most structurally involved of the agreements read: the highest of $40, 2% of the balance, or a tiered calculation that takes 1% of the balance net of interest up to $20,000 and rising percentages in brackets above that, then adds the billed interest back. Cited specifically because it shows a flat percentage existing as one branch inside the formula rather than as an alternative to it. Checked 2026-09-19
  9. Appendix M1 to 12 CFR Part 1026 — Repayment disclosures The prescribed method behind the statement disclosures, and its tolerances: a minimum-payment repayment estimate is accurate within two months either way (paragraph (b)(5)), and the 36-month payment within 10 percent either way (paragraph (d)(4)). Those tolerances are why a statement figure and this page can legitimately differ. Checked 2026-09-19
  10. Appendix M2 to 12 CFR Part 1026 — Sample calculations The Bureau's own worked illustration, which assumes a minimum payment formula of "2 percent of the outstanding balance or $20, whichever is greater" on a $1,000 balance. Cited to show that the flat-percentage model this calculator can compute is a recognised illustrative convention — and nothing more than that. It is an example inside a disclosure appendix, not a mandated formula. Checked 2026-09-19
  11. Bank of America — Customized Cash Rewards agreement, minimum payment clause (30 June 2026) A minimum built as 1% of the new balance plus new interest plus any late fee, with that sum rounded DOWN to the dollar and floored at $35. Cited alongside the others to show that the floor's placement and the rounding direction differ between issuers, which is why this page does not reproduce any single formula. Checked 2026-09-19
  12. BLS — Consumer Expenditures, 2024 (news release) Every measured spending figure on this page, for reference year 2024, released 19 December 2025. Average annual expenditures per consumer unit of $78,535 against average income before taxes of $104,207. Housing $26,266 (33.4% of spending), transportation $13,318 (17.0%), food $10,169 (12.9%), personal insurance and pensions $9,797 (12.5%), healthcare $6,197 (7.9%), entertainment $3,609 (4.6%), apparel and services $2,001 (2.5%). Food at home $6,224 and food away from home $3,945, which is the basis for treating restaurant spending as discretionary. The derived figures this page quotes are arithmetic on those published numbers: the four need-like categories total $55,950, which is 71.2% of spending and 53.7% of pre-tax income; housing, transportation and food together are 63.4% of spending; total spending is 75.4% of pre-tax income. The release notes that shares do not sum to 100.0 because of rounding. Checked 2026-09-19
  13. BLS — Consumer Price Index: Questions and Answers What the CPI measures and what it excludes: an average of prices across more than 200 item categories in eight major groups, for a defined urban population — CPI-U covering over 90% of the US population and CPI-W about 30%, with rural, farm and institutional households outside both. It also supports this page's statement that a general index is not a description of an individual household's experience, in the BLS's own words that the CPI "does not necessarily measure your own experience with price change". It establishes no rate of inflation, and nothing on this page is derived from it numerically. Checked 2026-09-19
  14. BLS — Using the Consumer Price Index for escalation The conventional use of a price index to adjust dollar values between periods, and the specific cautions this page repeats: that the US City Average is recommended over local-area series, that local series carry substantially larger sampling errors, and that seasonally adjusted data are inappropriate for escalation because they remain subject to revision for up to five years. It backs the limitation that adjusting a contract requires a measured series rather than the assumed constant rate used here. Checked 2026-09-19
  15. Census Bureau — About the Annual Retail Trade Survey What the benchmark table is and what became of it. ARTS "produced national estimates of total annual sales, e-commerce sales, sales taxes, end-of-year inventories, purchases, total operating expenses, and gross margins for retail businesses located in the United States", covering employer businesses in the retail trade sector in the 50 states and the District of Columbia, with nonemployers included "through imputation or administrative data provided by other federal agencies", published "at an industry level" using NAICS and released "approximately 15 months after the reference year had concluded". It also records that ARTS "transitioned to the Annual Integrated Economic Survey (AIES)", whose data collection "began in March 2024" — which is why 2022 is the most recent year this page can quote from the ARTS gross margin tables. Checked 2026-09-19
  16. Census Bureau — Annual Retail Trade Survey: gross margin as a percentage of sales Every retail benchmark quoted on this page, read from the published table "Estimated Annual Gross Margin as a Percentage of Sales of U.S. Retail Firms by Kind of Business: 1993-2022" for the 2022 column: retail total 31.6%, retail excluding motor vehicle and parts dealers 33.4%, GAFO 35.5%, automobile dealers 21.8%, warehouse clubs and supercenters 23.0%, grocery stores 28.0%, pharmacies and drug stores 28.1%, electronics and appliance stores 29.5%, beer, wine and liquor stores 31.0%, health and personal care stores 33.1%, department stores 34.7%, building materials and supplies dealers 35.9%, electronic shopping and mail-order houses 39.7%, sporting goods, hobby, musical instrument and book stores 45.4%, clothing stores 50.8%, furniture and home furnishings stores 51.0% and shoe stores 51.0%. These are margins — shares of sales — which is the point they are quoted for; the markup equivalents shown alongside them were computed by this site’s engine. The table marks several detailed industries "S", an estimate that "does not meet publication standards", and none of those is quoted here. The survey states that estimates are national, cover employer businesses in the 50 states and DC, are published at an industry level under NAICS, and "have not been adjusted for price changes". Checked 2026-09-19
  17. CFPB — An essential guide to building an emergency fund The central editorial claim of this page: that no months-of-expenses benchmark is published as guidance. The CFPB’s guide names no such figure, stating instead that "The amount you need to have in an emergency savings fund depends on your situation", and suggests sizing the fund from what your own past unplanned expenses cost — "Think about the most common kind of unexpected expenses you’ve had in the past and how much they cost". It also supports the definition of an emergency fund used here as "a cash reserve that’s specifically set aside for unplanned expenses or financial emergencies", and the three criteria quoted for where to keep it: "safe, accessible, and in a place where you’re not tempted to spend it on non-emergencies". It establishes no target figure, and no number on this page is derived from it. Checked 2026-09-19
  18. CFPB — Budgeting: how to create a budget and stick with it The claim that no US consumer-protection agency publishes a percentage split for budgeting. This page was checked directly and names no percentages whatsoever — no 50/30/20 and no numeric proportion for needs, wants or saving. Its method is process-based: record all income including multiple jobs and benefits, log and sort spending by category, map bill due dates, then consolidate into a worksheet to see whether income covers expenses "while also having enough to save". Allocation decisions are left to the reader throughout. It is cited to support a statement about what guidance does NOT exist, which is the page’s editorial spine. Checked 2026-09-19
  19. CFPB — Should I use a biweekly mortgage payment plan? That biweekly plans result in the equivalent of one extra monthly payment a year, that some services charge fees to arrange them, and that the same effect can be achieved by paying extra directly — the basis for separating the frequency effect from the extra-payment effect on this page. Checked 2026-09-19
  20. CFPB — What is the difference between a mortgage interest rate and an APR? Why the rate entered here is the nominal interest rate rather than the APR, which also includes fees and other costs of credit. Checked 2026-09-19
  21. CFPB final rule, 86 FR 60360 — General QM definition amendments The amendment that removed the 43% DTI ceiling and Appendix Q in favour of a price-based test, and its effective dates. Checked 2026-09-19
  22. Consumer Financial Protection Bureau — How to reduce your debt (archived blog, 16 July 2019) The CFPB's own description of both orderings — the highest-interest-rate-first approach and the smallest-balance-first "snowball" — and its position that the reader should choose between them based on their own situation. Cited for that framing only. It is archived content rather than current CFPB guidance, it endorses neither method, and it cites no research for the motivational aside it makes about the snowball. Checked 2026-09-19
  23. Consumer Financial Protection Bureau — Owning a home: loan options Loan programme differences, including why FHA and VA ratios are not modelled here. Checked 2026-09-18
  24. Consumer Financial Protection Bureau — What is a debt-to-income ratio? How debt-to-income ratio is defined, which obligations count toward it, and the distinction between front-end and back-end. Note that this source does not establish the 36% or 43% figures as requirements. Checked 2026-09-19
  25. Consumer Financial Protection Bureau — What is amortization? The definition of amortisation and how a level payment divides between interest and principal over a loan term. Checked 2026-09-19
  26. Consumer Financial Protection Bureau — What is private mortgage insurance? How PMI is charged, and typical premium ranges. Checked 2026-09-18
  27. Discover — Prime cardmember agreement, minimum payment clause (30 June 2026) A minimum of any past-due amount plus the greatest of $35, 2% of the new balance, or $20 plus interest charges and certain fees, rounded up to the nearest dollar. Notable because the dollar figure here competes as one prong rather than acting as a floor beneath the others. Checked 2026-09-19
  28. FDIC — Deposit insurance The scope of federal deposit insurance, including the standard $250,000 limit per depositor, per insured bank, per ownership category — the basis for flagging that a large cash savings target held at a single institution may be partly uninsured. It says nothing about rates of return. Checked 2026-09-19
  29. FDIC FIL-2-2003 — Credit Card Lending: Account Management and Loss Allowance Guidance (text of the interagency guidance) The readable text of the same 2003 interagency guidance, containing the operative sentence: "The Agencies expect lenders to require minimum payments that will amortize the current balance over a reasonable period." Cited because the Federal Reserve's own copy of the attachment is a scanned image. Still guidance, not a rule. Checked 2026-09-19
  30. Federal Reserve — Economic Well-Being of U.S. Households in 2025 Every population figure quoted on this page, all from the survey fielded 17–28 October 2025: that 55 percent of adults said they had set aside money to cover three months of expenses (unchanged from 2024, down from 59 percent in 2021), that 30 percent could not cover three months by any means, that 63 percent could cover a hypothetical $400 emergency expense with cash or its equivalent while 12 percent could not pay it at all, and the breakdown by family income from 21 percent under $25,000 to 75 percent at $100,000 or more. These are measurements of how households answered a survey, and this page does not use them to imply what any reader’s target should be. Checked 2026-09-19
  31. Federal Reserve — SHED 2025: Description of the Survey What the figures above are and are not. The survey was fielded 17–28 October 2025 with a final sample of 12,934 respondents drawn from a probability-based, address-sampled online panel and weighted to March 2025 CPS benchmarks, representing an estimated 265 million US adults. It reports no margin of error, giving a design effect of 1.14 instead. Its own stated limitations are cited here in support of treating these percentages as context rather than as a benchmark: address-based sampling "likely misses homeless populations", non-English speakers may not participate, and an online-only survey may over-represent adults comfortable with the internet. Checked 2026-09-19
  32. Federal Reserve Board — G.19 Consumer Credit release (8 September 2026) Average credit card interest rates: 20.94% across all accounts and 22.15% across accounts assessed interest, both for the second quarter of 2026. The distinction matters — the all-accounts figure is diluted by accounts paid in full each month. These are market averages and establish nothing about any individual rate. Checked 2026-09-19
  33. Federal Reserve SR 03-1 — Account Management and Loss Allowance Methodology for Credit Card Lending (supervisory guidance, 8 January 2003) The interagency supervisory guidance in which the banking agencies state they expect lenders to require minimum payments that amortise the balance over a reasonable period, and that prolonged negative amortisation raises safety-and-soundness concerns. This is GUIDANCE applied through examination, not a regulation, and it sets no percentage — but it is the reason nearly every modern agreement includes a term covering interest plus principal. Checked 2026-09-19
  34. Homeowners Protection Act of 1998, 12 U.S.C. §4902 — termination of private mortgage insurance The statutory 78% automatic termination and 80% request thresholds that determine when PMI stops being part of the payment. Checked 2026-09-18
  35. Income Tax in Scotland — GOV.UK Confirmation that Scotland sets separate Income Tax bands, which this calculator does not apply. Checked 2026-09-21
  36. Income Tax rates and Personal Allowances — GOV.UK The £12,570 Personal Allowance, the 20/40/45% band rates and their thresholds, and the withdrawal of the allowance above £100,000. Checked 2026-09-21
  37. Investor.gov (SEC) — Compound Interest Calculator The SEC's own compound interest tool and its explanation of how principal, contributions, rate and compounding frequency combine over time. It establishes the mechanics of compounding and the convention of projecting a chosen rate; it does not establish any expected rate of return, and it does not provide the inflation adjustment this page treats as the headline figure. Checked 2026-09-19
  38. Investor.gov (SEC) — Savings Goal Calculator The SEC's own implementation of the same future-value-solved-for-contribution calculation, useful as an independent check on the arithmetic. It does not establish any particular rate of return as available, and does not address deposit timing or the rounding convention used here. Checked 2026-09-19
  39. IRS Publication 334 — Testing Gross Profit Accuracy The claim that the vocabulary itself is ambiguous, quoted from the "Figuring Gross Profit" chapter. The instruction to "divide gross profit by net receipts", the resulting percentage being compared to "your markup policy", and the example whose net receipts are $300,000, cost of goods sold $200,000 and gross profit $100,000, described as a business that marks up "so that you will realize a gross profit of 33 1/3 % on its sales" and concluding "The resulting 33 1/3 % confirms your markup percentage of 33 1/3 %." Profit as a share of cost on those same figures is 50%, computed by this site’s engine rather than taken from the publication. Cited to establish that one figure is called both things in federal guidance, not to assert an error: the passage states its own divisor explicitly. It backs no figure this page calculates. Checked 2026-09-19
  40. JPMorgan Chase — cardmember agreement, minimum payment clause (June 2026) Chase's minimum as past-due amounts plus the larger of $40 or the sum of 1% of the new balance plus billed periodic interest and late fees. One of six agreements read to establish that issuers use a greatest-of structure with an interest-bearing term rather than a flat percentage. Checked 2026-09-19
  41. National Insurance rates and categories — GOV.UK The 8% main rate and 2% rate above the Upper Earnings Limit, the £242 weekly Primary Threshold and £967 weekly Upper Earnings Limit, and the category letters. Checked 2026-09-21
  42. Repaying your student loan: what you pay — GOV.UK The Plan 1, 2, 4 and 5 thresholds at 9%, and the £21,000 Postgraduate Loan threshold at 6%. Checked 2026-09-21
  43. U.S. Bank — cardmember agreement, minimum payment clause (effective 30 June 2026) A "base minimum payment" of the greater of $40 or 1% of the balance, with interest charges and fees added on top of that floored base and the total rounded up. A materially different construction from Bank of America's despite similar components. Checked 2026-09-19
  44. US Small Business Administration — Plan your business: break-even analysis The three formulas this page implements, quoted verbatim from the "Tips and tricks" guidance in the break-even section: "Break-even point (units) = fixed costs ÷ (sales price per unit – variable cost per unit)", "Break-even point (sales dollars) = fixed costs ÷ contribution margin", and "Contribution margin = (sale price per unit – variable cost per unit) ÷ sale price per unit". Also the definition of fixed costs as "costs incurred during a specific period of time that do not change with the increase or decrease in production or services", the examples given for them ("rental lease payments, salaries, property taxes, insurance, interest, and depreciation"), the monthly basis and the instruction to divide a quarterly cost by four, and the semi-variable category — "costs composed of a mixture of both fixed and variable components" whose recommended treatment is "to separate out the part that is variable from the part that is fixed", with examples "monthly telephone services, repairs, indirect materials, indirect labor, fuel, and power". Cited for the method and the definitions only. The second formula names "contribution margin" where the third defines that phrase as a ratio, so the two sentences use the same words for the per-unit dollars and for the percentage; this page notes that ambiguity, computes revenue as units multiplied by price instead, and states the difference the choice makes. No figure on this page is taken from the SBA — every one was produced by this site’s engine. Checked 2026-09-19
  45. Wells Fargo — Active Cash card agreement, minimum payment clause (June 2026) A minimum of past-due amounts plus the greater of (1% of the new balance plus billed interest and certain fees) or $25, rounded UP to the next whole dollar. Cited from the issuer's own current page rather than the database copy, which is an outdated capture. Checked 2026-09-19

Corrections

If a number here is wrong,
we want to know.

These are mathematical estimates, not financial advice, and the arithmetic being tested does not make every assumption behind it right for your situation. Real outcomes vary with terms, fees, jurisdiction and timing.

If a calculation disagrees with your loan statement or your own working, that is worth reporting — a reproducible discrepancy is the most useful thing anyone can send us, and a tool that produces one gets fixed rather than explained away. Where a correction changes a published figure, the page's revision date changes with it.

This page last reviewed September 22, 2026. Tests last reconciled 2026-09-22.