Compound Interest Calculator
See what a one-time amount grows into with compounding, and how much of the result is interest at the rate and frequency you choose.
How compounding works
Compounding means interest starts earning interest. Each period the balance grows, and the next period's interest is worked out on that bigger balance, so the curve gets steeper the longer you leave it.
More frequent compounding raises the result a little for the same rate, which is why the frequency option matters. For monthly contributions rather than a lump sum, see our finance calculators.
Common questions
What is the difference between simple and compound interest?
Simple interest is worked out only on the original amount, while compound interest is worked out on the amount plus the interest already added. Over long periods compounding pulls far ahead.
Does compounding frequency really matter?
It nudges the result up: monthly compounding beats yearly at the same rate, because interest is added back sooner and starts earning earlier. The effect grows with the rate and the time.
What rate should I use?
Use whatever your account or instrument actually pays. The tool stays neutral and just compounds the rate you enter, so a realistic figure gives a realistic result.