Compound Interest Calculator

How to use the compound interest calculator

1. Fill in the fields — they start with a worked example.
2. Read the answer, and the arithmetic shown beneath it.
3. Copy the results, or adjust the inputs to compare scenarios.

About this tool

Compound interest pays interest on interest, so the balance grows on a curve rather than a line. Two things drive it: time, which matters more than the rate, and how often interest is added.

The split between what you paid in and what the interest earned is shown separately, because that ratio is the whole argument for starting early. Over long periods the interest can exceed the contributions; over short ones it rarely does.

The projection assumes a constant rate. Real investments do not have one, and inflation reduces what the final figure buys — treat the result as arithmetic, not a forecast.

Common uses

• Projecting a savings account over several years.
• Seeing what regular contributions add up to.
• Comparing compounding frequencies on the same rate.

Frequently asked questions

How much does compounding frequency matter?

Less than people expect. At 6%, monthly compounding beats annual by about 0.17 percentage points of effective yield — real, but far smaller than the effect of an extra year.

Does this account for inflation or tax?

No. It is the raw arithmetic. Both reduce what the final figure is actually worth.