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OZO Compound Interest Calculator

Free Compound Interest Calculator

See how your savings grow with compound interest and regular monthly contributions, with a year-by-year breakdown.

  • Free forever
  • No signup
  • Instant results
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Enter an amount, rate and number of years.

How to calculate compound interest

  1. 1

    Enter what you start with

    Type the amount you have saved or invested today.

  2. 2

    Add monthly contributions

    Optionally enter how much you will add every month.

  3. 3

    Set the rate and time

    Enter the annual interest rate, the number of years and how often interest compounds.

  4. 4

    See the growth

    Read the final balance, the interest earned and what you paid in, then open the year-by-year table.

Why compound interest matters

Because interest earns interest, money grows slowly at first and much faster later. Starting early and adding regularly usually beats trying to find a slightly higher rate. The year-by-year table shows the moment when the interest earned each year overtakes your own contributions.

How this calculator works

Contributions are added at the end of every month. Interest is applied using the monthly equivalent of the chosen compounding frequency (yearly, quarterly, monthly or daily), so every option is directly comparable.

Paying interest rather than earning it? The loan calculator shows the same maths working against you.

Frequently asked questions

What is compound interest?

Interest earned on both your original money and the interest it has already earned. Each period’s interest is added to the balance, so the next period earns interest on a bigger amount and growth speeds up over time.

What is the compound interest formula?

Without contributions, the final amount is P × (1 + r ÷ n)^(n × t): P is the starting amount, r the annual rate, n how many times a year interest compounds and t the number of years. 1,000 at 5% compounded yearly for 10 years grows to 1,628.89.

Does compounding frequency matter?

Yes, a little. The more often interest compounds, the more you earn at the same headline rate, but the difference between monthly and daily compounding is small. The rate and the time you stay invested matter far more.

Are returns guaranteed?

Only for fixed-rate savings. Investment returns vary from year to year and can be negative; treat the result as an illustration, not a promise, and remember inflation and tax.

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