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Interest & Investment Calculator

Math

Compound and simple interest, savings goals, CD maturity, Rule of 72, APR to APY, real and tax-equivalent returns, dividend yield, present and future value, and annuity payouts in one calculator

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About Interest & Investment Calculator

Eleven of the interest and return formulas people look up most, on one page instead of eleven: compound interest with optional monthly contributions and a year-by-year table, simple interest, how long a savings goal takes (or what to save each month), CD maturity value with early-withdrawal payout, the Rule of 72 checked against the exact doubling time, APR to APY in both directions, inflation-adjusted real return via the Fisher equation, tax-equivalent yield for municipal bonds, dividend yield and payout ratio, present and future value, and fixed annuity payouts. Each mode uses the standard textbook formula and shows its inputs and result plainly, so you can check the math or reuse it in a spreadsheet. It does not pull live rates or account for fees and taxes beyond what you enter, and it is a calculator, not financial advice.

How to use Interest & Investment Calculator

  • 1.Pick a calculation from the Growth, Rates or Time value groups; the URL updates so you can share that exact calculator.
  • 2.Enter the principal, rate, term and compounding frequency (or whichever inputs that mode asks for); results update as you type.
  • 3.Compare scenarios by changing one input at a time, for example monthly versus daily compounding, or a 4% versus 5% rate.
  • 4.Move between related modes: work out an APY in APR ↔ APY, then use it in Compound interest or Savings goal.

Frequently asked questions

What is the difference between simple and compound interest?
Simple interest is paid only on the original principal. Compound interest is also paid on interest already earned, so the balance grows faster the more often it compounds and the longer it runs.
What is the difference between APR and APY?
APR is the nominal annual rate before compounding; APY is the effective rate after compounding over a year. A 5% APR compounded monthly is about a 5.12% APY. Savings accounts usually quote APY, loans usually quote APR.
How accurate is the Rule of 72?
It is a mental-math shortcut that is closest for rates between about 6% and 10%. The Rule of 72 mode shows the exact logarithmic doubling time next to the estimate so you can see the gap.
Does it account for inflation or taxes?
Only where you ask it to: the real-return mode adjusts for inflation and the tax-equivalent yield mode for marginal tax rates. Other modes compute nominal, pre-tax figures.
Why did an old Utilix tool page redirect me here?
Utilix merged several single-purpose tools into the Interest & Investment Calculator. Each old URL now opens this page with its mode preselected (via ?mode=<old-tool-slug>), so bookmarks and links keep working. The old tools' REST endpoints, Node.js and Python SDK functions, and MCP tools are unchanged.

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