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Compound Interest Calculator

Project growth with compounding and contributions.

Use the Compound Interest Calculator tool

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What this compound interest calculator does

Compound Interest Calculator projects a balance from a starting principal, a constant annual rate, a term and an optional monthly contribution. It reports the future value, total money contributed, interest earned and the effective annual rate.

The schedule shows the balance at the end of each year, split into contributions and interest, so the point where growth starts to outpace deposits is visible. Figures are illustrative: they assume a constant rate with no tax, fees or inflation.

Why use it

  • See how much of a future balance comes from interest.
  • Compare monthly and annual compounding at the same rate.
  • Test the effect of adding a monthly contribution.

How to use it

  1. 1Enter the starting amount and annual rate.
  2. 2Set the term and compounding frequency.
  3. 3Add a monthly contribution if you plan to deposit regularly.

Worked examples

Lump sum

Input

10,000 at 7% compounded monthly for 10 years

Output

About 20,096.61 · interest about 10,096.61

With contributions

Input

1,000 at 6% plus 200 per month for 5 years

Output

A larger balance split between 12,000 contributed and the interest earned

Common mistakes

  • Entering a monthly rate where an annual rate is expected.
  • Assuming a fixed rate is a forecast; markets and savings rates change.
  • Ignoring tax on interest, which reduces the effective return.

Frequently asked questions

What does compounding frequency change?
More frequent compounding applies interest to a slightly larger balance each period. The effective annual rate rises, but the difference between monthly and daily is small at typical rates.
Are contributions added at the start or end of the month?
The calculation treats them as end-of-month deposits, which is the conservative assumption.
Is this financial advice?
No. It is arithmetic using the values you enter. It does not account for risk, inflation, taxes or fees.

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