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Worked example · edit any number
Borrow $ at % for years.
- r = 6.5% ÷ 12 = 0.5417% a month
- n = 5 × 12 = 60 payments
- (1 + r)ⁿ = 1.3828
- M = P × r(1+r)ⁿ ÷ ((1+r)ⁿ − 1)
- $489.15a month
Over 5 years you pay $4,349.22 in interest.
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Numbers you can actually trust
Every result here is a tested program — not a language-model guess. That's the difference between a calculator and asking an AI to "do the math."
- Tested, not guessed 13,700+ automated tests, and 342 of 342 calculators checked against independent sources. Deterministic math — never a hallucinated number.
- Shows the work Every formula, worked example, and source is on the page — not a black box.
- Sourced & checkable Where a formula has an authoritative source, it’s cited on the page — so you can verify it yourself.
- Private by default Runs in your browser. Your inputs never leave your device. No account.
Latest guides
All 157 →-
Finance · 4 min
How to Use an Amortization Calculator
A step-by-step way to use an amortization calculator: enter the loan, change one input at a time, co…
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Finance · 4 min
APR vs Interest Rate: What's the Difference?
APR counts certain upfront fees as well as interest. A worked $300,000 example finds the APR by iter…
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Health & Fitness · 6 min
What Your BMI Really Means (And Its Limitations)
BMI cannot tell muscle from fat, misses about half of people with excess body fat at common cutoffs,…
Questions, answered
- Are the calculators free?
- Yes — all 342 of them, with no account, no sign-up, and no paywall.
- Can I trust the results?
- Every formula is a tested program, not a language-model guess — backed by 13,700+ automated tests (342 of 342 calculators are also checked against independent sources), with the formula and its source shown on each page. The math is deterministic: the same inputs always give the same answer. See how we build and verify calculators on our methodology page.
- Is my data private?
- Completely. Every calculation runs inside your browser — your numbers are never sent to a server, and nothing is stored about you.
- Do they work on mobile?
- Yes. Every calculator is fully responsive and loads fast, because pages are static and ship almost no JavaScript.