Plainsum

Financial calculators that show their work

18 free calculators for loans, mortgages, savings, retirement and taxes. Results update as you type, and every one explains how the number was worked out.

Loans & mortgages

MortgageMonthly cost of a home with taxes, insurance, PMI and HOA.
AmortizationFull payment schedule with extra monthly, yearly or one-time payments.
Mortgage PayoffHow extra payments shorten the loan you already have.
Auto LoanCar payment with trade-in, sales tax and fees, or the price you can afford.
LoanMonthly payments, a single payoff at the end, or a bond's price today.
PaymentFind the monthly payment, or how long a payment takes to clear a loan.
Interest RateFind the real rate behind a loan from its payment.

Saving & investing

Compound InterestGrowth at any compounding frequency, and equivalent rates.
InterestSavings growth with deposits, taxes and inflation.
InvestmentEnd balance, or the contribution, return or start needed for a goal.
Finance (TVM)Time-value-of-money solver for N, I/Y, PV, PMT and FV.

Retirement

RetirementWill your savings last? What to save to close the gap.
401(k)401(k) balance at retirement and whether you get the full match.

Income & taxes

Income Tax2026 federal income tax, refund or amount owed, by bracket.
SalaryConvert pay between hourly, weekly, monthly and yearly.
Sales TaxAdd tax to a price, back it out of a total, or find the rate.

Prices & currency

InflationFuture prices and lost buying power at any inflation rate.
Currency ConverterConvert between major currencies with your own rate.
Live results

No Calculate button. Change a number and everything updates.

Shows the math

Each calculator states its formula and assumptions under the results, with a worked example.

Private by design

The numbers you enter are calculated in your browser and never sent to us.