Compound Interest Calculator
Watch your money grow. See how compound interest, contributions, and time work together.
Compare frequencies
Pre-tax estimates. Returns are not guaranteed and past performance does not predict future results.
Growth over time
What is Compound Interest Calculator?
Compound interest is interest calculated on both the initial principal and the accumulated interest from previous periods. Often described as 'interest on interest', it causes savings and investments to grow at an accelerating rate over time. This calculator shows your final balance, total contributions, and total interest earned across different compounding frequencies.
How to use it
- Enter your starting amount and the expected annual interest rate.
- Choose how long you plan to invest and the compounding frequency.
- Optionally add a regular monthly contribution.
- Review your final balance, growth chart, and a frequency comparison table.
Compound interest formula
Future value A = P(1 + r/n)^(n·t) + PMT × [((1 + r/n)^(n·t) − 1) ÷ (r/n)], where P is principal, r the annual rate, n the compounding periods per year, t the years, and PMT the regular contribution per period.
Frequently asked questions
Simple interest is calculated only on the original principal. Compound interest is calculated on the principal plus accumulated interest, so your balance grows faster the longer it is invested.
More frequent compounding (monthly vs yearly) grows your balance slightly faster because interest is added and starts earning more often. The difference is small at low rates but grows over long periods.
Historical stock market returns have averaged around 7–10% per year before inflation, but returns vary. Use a conservative estimate for planning, and remember past performance does not guarantee future results.
Inflation reduces the real purchasing power of your money. To see real growth, subtract expected inflation (often 2–3%) from your assumed return rate.
With PMT set to 0, the calculator uses the basic compound formula A = P(1 + r/n)^(n·t). This shows growth from your initial principal only.
Interest and investment gains are often taxed depending on your country and account type. This calculator shows pre-tax growth; consult a tax advisor for after-tax returns.
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