The library
Every calculator,
grouped by the question.
Each tool shows the formula it uses, states what it assumes, and gives you the schedule or the working underneath the answer. Nothing is behind a sign-up, and the arithmetic runs in your browser.
Mortgage & Home
Work out payments, affordability, amortisation and the cost of paying early.
- Mortgage Calculator Work out the monthly payment on a home loan, see how much of it is interest, and read the full amortisation schedule underneath.
- Mortgage Affordability Calculator Work out the most expensive home your income and existing debts support, using the ratios lenders conventionally apply — and see which of the two actually limits you.
Loans & Debt
Payments, interest, amortisation and payoff strategies for any fixed-rate loan.
- Amortization Calculator See where every payment goes — interest, principal and balance, payment by payment — and what actually changes when you pay more often or pay more.
- Debt-to-Income Ratio Calculator Work out the two ratios lenders actually look at — housing alone, and every debt together — and see how much of your monthly obligations would need to clear to reach the conventional 36%.
- Credit Card Payoff Calculator Work out how long a card balance takes to clear and what the interest costs — and what changes if the payment stays the same every month instead of shrinking with the balance.
- Debt Payoff Calculator Price the snowball against the avalanche on your own debts — and find out whether the choice is worth anything at all, which is often less than the argument about it suggests.
Saving & Investing
Compound growth, contributions, returns, inflation and goal planning.
- Compound Interest Calculator Project what regular investing could grow to over decades — and see the same figure in today's money, which is the number that tells you what it would actually buy.
- Savings Goal Calculator Work out what you would have to put aside each period to reach a specific amount by a specific date — and what the rate you assume is really doing to that figure.
- Investment Return Calculator Work out what an investment actually returned, both in total and per year — and see why the total on its own cannot be compared with anything.
- Inflation Calculator See what a sum would need to grow to just to stand still — and what it will actually buy if it does not. Two figures, both true, running in opposite directions.
Salary & Pay
Convert pay periods, compute overtime, raises and take-home pay.
Business
Margins, markup, break-even, ROI and business financing.
- Margin & Markup Calculator Margin is profit against the price; markup is the same profit against the cost. Enter what an item costs and what it sells for to get both, then set a target to see the two different prices it implies.
- Break-Even Calculator How many units cover your fixed costs before anything is profit. Enter the monthly fixed costs, the price and the variable cost per unit to get the volume, the revenue it takes, and what a target profit would need on top.
Everyday Money
Percentages, discounts, budgets, savings goals, net worth and inflation.
- Budget Calculator Sort a month of take-home pay into needs, wants and saving, see the three shares it actually produces, and compare them against the 50/30/20 framework and what US households measurably spend.
- Emergency Fund Calculator Work out what a cash reserve of the size you choose actually costs, how much of it you already have, and how long the rest takes at the amount you can genuinely put aside.
The standard
What every tool here has to do before it ships.
- Verified against independent values
- Every formula is tested against figures computed separately from the code that implements it. A calculator that agrees only with itself has not been checked.
- Assumptions stated, not buried
- Each page lists what its maths assumes and what it deliberately does not model. Where a rule is an industry convention rather than law, it says so.
- Sources cited with dates
- Figures that come from a regulator or statute link to the source and carry the date it was last checked, so you can tell whether it is still current.
- Computed on your device
- The arithmetic runs in your browser; there is no calculation endpoint on the server and no calculation is stored. The one exception, explained