How we calculate

All Numfino calculators share one calculation engine, which runs in your browser. This page lists the conventions it uses so you can compare our results with a lender's or a spreadsheet's.

Loans and mortgages

Payments use the standard level-payment (annuity) formula M = P · r / (1 − (1 + r)^−n), where r is the annual rate divided by 12 and n the number of monthly payments. Interest is charged each month on the remaining balance (a reducing balance), which is how most mortgages, car loans and personal loans work.

Amortization schedules are simulated month by month, so the final payment absorbs rounding. Taxes, insurance and fees are added on top of principal and interest where a calculator asks for them; lender-specific fees, insurance products and variable-rate resets are not modelled.

Saving and investing

Savings calculators convert the annual rate to an equivalent monthly rate for the compounding frequency you choose: (1 + rate / f)^(f / 12) − 1. Contributions are added at the end of each month. Investment returns are shown as steady averages; real markets go up and down, and fees and taxes reduce returns.

Annualized return and CAGR use (end / start)^(1 / years) − 1. Present value discounts with (1 + r)^−t.

Options for extra precision

Credit card calculators can charge interest the way most issuers do: a daily periodic rate (APR ÷ 365) compounded every day, instead of the simpler APR ÷ 12 per month. Minimum payments can follow either a percent of the balance or the common "interest plus a percent of the balance" formula, with a floor.

The mortgage calculator adds private mortgage insurance when the down payment is under 20% and drops it once the balance reaches 78% of the original price, the point at which it must be cancelled on most US conventional loans. The biweekly calculator can model a lender that charges interest every two weeks (26 periods a year) as well as the common estimate of one extra monthly payment a year.

Savings calculators let contributions arrive at the start or the end of each month (annuity due or ordinary annuity) and grow by a set percentage each year. Payoff dates count forward from the current month.

How we test the formulas

Every release is checked against independent reference values: spreadsheet functions such as PMT, FV, IRR and YIELD, the actuarial APR method used in US Regulation Z disclosures, and textbook depreciation schedules. A release is blocked if any result drifts from the reference.

Currencies and rounding

You can switch the currency on any calculator; this changes formatting only, not the numbers. Default examples are scaled to each language's usual currency. Displayed figures are rounded; internal calculations keep full precision.

Limits

Results are estimates for planning and education. They are not offers of credit, tax advice or investment recommendations. Rules on taxes, fees and lending limits vary by country and change over time, so check final figures with your lender or a qualified adviser.