Zerdly

Compound Interest Calculator

Calculate compound interest growth on savings or investments with monthly, quarterly or yearly contributions, free and instant in your browser.

100% FreeRuns in your browserBasic
How to use this calculator

Enter Values

Minimum 0

Minimum 0

Minimum 0

Minimum 1

Enter your values and press Calculate to see results.

Before you rely on this: First-pass guide only. Verify safety-critical or regulated work against the relevant standards, your project requirements and a qualified professional.

How to use this calculator

  1. Enter the starting principal, the annual interest rate and the number of years.
  2. Optionally set how many times a year it compounds (defaults to monthly).
  3. Press Calculate to see the final balance and the interest earned.

How it works

Compound interest earns interest on both your original amount and the interest already added. The formula is A = P(1 + r/n)^(nt), where P is the principal, r the annual rate, n the times it compounds per year and t the number of years.

Compounding more often (monthly rather than yearly) slightly increases the final balance.

Worked example

$10,000 at 5% for 10 years, compounded monthly. A = 10,000 × (1 + 0.05/12)^(12×10) ≈ $16,470 — about $6,470 of interest.

Common mistakes

  • Setting the compounding frequency to 1 (yearly) when your account compounds monthly — use 12.
  • Entering the rate as a decimal (0.05) instead of a percent (5).
  • Expecting regular deposits to be included — this is a lump sum only; use the savings goal calculator for contributions.

Frequently asked questions

Does this include regular deposits?

No — it assumes a single lump sum with no further deposits or withdrawals.

Which compounding frequency should I pick?

Many savings accounts compound monthly; check your product's terms and conditions.

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Cite this tool

Zerdly. (2026). Compound Interest Calculator. Retrieved from https://www.zerdly.com/tools/compound-interest-calculator/

Tip: Enter any known values to calculate the remaining results.

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