Free finance calculators that show their math
Free, fast, no signup. Every calculator explains its formula in plain English, cites an authoritative source, and is built US-first - real tax rules, real dollar defaults.
17 live calculators
Debt
- Debt Snowball vs Avalanche CalculatorCompare both payoff methods side by side - see your debt-free date, total interest, and which method wins for your exact debts.
- Credit Card Minimum Payment CalculatorThe true declining-minimum trap: years and total interest if you only pay the minimum.
- Credit Card Payoff CalculatorFixed-payment credit card payoff time, total interest, final payment, and the monthly payment needed for a target date.
Savings
- HYSA vs CD vs Treasury Bill CalculatorAfter-tax 3-way comparison that models the state-tax exemption on Treasury interest.
- CD Ladder CalculatorBuild a CD ladder with your own rates - maturity schedule, blended APY, and how much stays liquid each year.
- Emergency Fund CalculatorA personalized target based on your real risk factors - not a flat 3-6 months.
Home
- Mortgage Extra Payment CalculatorExtra monthly, lump sum, and biweekly payments with your PMI removal date and dollars saved.
- Rent vs Buy CalculatorThe honest break-even: invests the renter's down payment, counts every cost, and compares net worth year by year.
- Home Sale Capital Gains CalculatorEstimate taxable home-sale gain with adjusted basis, selling costs, the $250k/$500k IRS exclusion, and depreciation recapture.
Retirement
- 401(k) Employer Match MaximizerReal match formulas including two-tier plans, per-paycheck breakdowns, and the early-max-out trap.
- Roth vs Traditional CalculatorWhich wins for your 401(k) or IRA - the honest comparison that invests the tax savings and shows your break-even retirement tax rate.
- Coast FIRE CalculatorFind the age you can stop saving for retirement - compound growth alone carries you to your FIRE number. Inflation-adjusted.
Free finance calculators built to be checked, not just used
CentsMath is a collection of free financial calculators for the money decisions US households actually face: paying off credit cards and loans, sizing an emergency fund, capturing a full 401(k) employer match, estimating quarterly taxes as a freelancer, comparing savings accounts against CDs and Treasury bills, and working out what a mortgage extra payment or a car trade-in really changes. Every tool is free, loads instantly, and asks for nothing - no signup, no email, no paywall, and nothing you type ever leaves your browser.
The math is shown, and it is tested
Most online calculators are black boxes: numbers in, verdict out, formula hidden. Every CentsMath calculator does the opposite. Each page explains its formula in plain English, walks through a fully worked example with realistic US numbers, and cites the primary source the math comes from - IRS worksheets, Consumer Financial Protection Bureau guidance, Department of Labor rules, or TreasuryDirect. Behind the pages, every calculation engine is covered by automated tests that check results against closed-form math and edge cases before anything ships. When tax brackets, contribution limits, or state rates change, the data lives in one reviewed place and is updated for the new year. See how we verify every calculator for the full editorial and testing process.
Built US-first
The defaults reflect real American finances: federal tax brackets and the standard deduction, Social Security wage bases, state income tax and vehicle sales tax differences, PMI rules under the Homeowners Protection Act, and APRs you will actually see on a US credit card statement. Where a state rule changes the answer - like the trade-in tax credit on a car purchase, or the state-tax exemption on Treasury interest - the calculator models your state instead of pretending the difference does not exist.
Honest limits
These are educational planning tools, not financial advice, and a calculator cannot know your full situation. Each page states its assumptions and simplifications out loud so you can judge whether they fit. If a number ever looks wrong, tell us - accuracy reports are fixed before anything else, because a calculator you cannot trust is worse than no calculator at all.