Money calculators
Each one gives you the formula, every period of the schedule, and a result you can export or print. Every calculation runs in your browser.
- Debt payoff — avalanche vs snowballCompare both methods against paying only the minimums. Full month-by-month schedule, chart, spreadsheet and printable PDF.Works in any currency. No jurisdiction rules involved.
- Mortgage overpayment — what paying extra removesSee exactly what an extra monthly payment takes off a mortgage, in months and in interest. Full schedule, chart, spreadsheet and printable PDF.US fixed-rate convention. The required payment matches the published figure to the cent.
- UK early repayment charge — is the charge worth paying?What an overpayment charge costs against the interest the overpayment removes. Full schedule, chart and spreadsheet.United Kingdom. Your allowance and charge are inputs — no lender’s terms are assumed.
- Coast FIRE — when saving becomes optionalHow much you need invested today for it to reach your retirement target on its own. Year-by-year projection, chart, spreadsheet and printable PDF.Everything in today’s money. Works in any currency.
The arithmetic behind them
Each one works a single calculation out from first principles, with real figures computed by the same engines the tools run.
- How long minimum payments take, and when they never finish — the one line that decides whether a card ever clears, and the balances where it does not
- Biweekly mortgage payments: what the thirteenth payment does — why 26 half-payments is 13 monthly ones, and what that one extra payment removes
- How credit card interest is actually calculated — the daily periodic rate, and why 22.99% costs 25.838%
- Why a 7% return is not 0.583% a month — one division that overstates thirty years by $50,424
- Where the 4% rule comes from — what Bengen and the Trinity Study actually tested, and what they did not
- What a coast number is, and what it is not — the assumption that moves the figure more than any other
Being built
Tools are added one at a time, each with its arithmetic tested against a published figure before it ships. Nothing appears here until it is finished and checked.
- Freelance and contractor rate
How to know these numbers are right
Every calculation is a tested function checked against published third-party figures, and the tests are public. The methodology page sets out the rounding policy, the verification approach, and a worked example you can repeat yourself.