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A little Napkin Math goes a long way

Quickly estimate budgets, FIRE timelines, loan payoffs, and real-world trade-offs — no spreadsheets required.

No sign-ups. No fees. No fine print.

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Start with one of these, then browse the full library.

Mortgage calculator

Estimate payments and see amortization over time.
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FIRE retirement

Project your savings rate and time to financial independence.
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Compound interest

Watch contributions and growth stack up over years.
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Savings rate

Quickly see whether your savings rate supports your goals.
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House affordability

Estimate how much house you can afford with a monthly budget.
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Credit card repayment

Estimate payoff time and total interest based on APR and payments.
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An investment in knowledge pays the best interest.
— Benjamin Franklin

How Napkin Math helps

Napkin Math is a library of fast, visual financial calculators that help you turn money questions into clear answers.Estimate budgets, compare mortgage payments, project FIRE timelines, and explore long-term trade-offs—all with transparent assumptions and interactive charts.