Compound Interest Calculator

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Find out what your money could grow to after years of compound returns, with or without monthly contributions.

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Result

Enter the amount, return and period.

Compounding means returns are added to your capital and start earning returns themselves. Growth is slow at first and then accelerates, which is why starting early matters.

Choose how often returns compound each year and add a fixed monthly contribution at the start or end of each month.

How it works

The effective monthly growth factor is derived from the annual rate and compounding frequency.
Growth is applied month by month and the monthly contribution is added at the chosen time.
Total growth = final balance − total contributed.
The effective annual rate shows the compounding effect: 12% compounded monthly is 12.68% effective.

Formulas

A = P × (1 + r ÷ k)^(k × t)
P = initial amount, r = annual rate, k = compounding per year, t = years
Effective rate = (1 + r ÷ k)^k − 1

Worked examples

10,000 at 5% a year for 10 years

Compounded yearly it grows to 16,288.95, so the growth is 6,288.95.

1,000 at 5% compounded monthly for 10 years

It grows to 1,647.01, a little more than yearly compounding (1,628.89) thanks to more frequent compounding.

Frequently asked questions

Simple vs compound interest?

Simple interest is earned on the original amount only. Compound interest is earned on the original amount plus accumulated returns.

Is the expected return guaranteed?

No. Market returns vary; the calculation assumes a constant rate for illustration.

Is inflation included?

No. For a rough real value, subtract expected inflation from the return.

Content last reviewed: November 1, 2026