Compound Interest Calculator

How your savings grow with compound interest, with or without monthly deposits.

Works in any currency.

Optional. Leave empty or 0 for none.

%

Balance after 10 years

50,969.84

Total you put in
34,000.00
Interest earned
16,969.84
Effective yearly rate
6.168%

10,000.00 plus 200.00 a month at 6% a year, compounded monthly, grows to 50,969.84 after 10 years. 16,969.84 of that is interest.

Year by year growth

YearAddedInterestBalance
12,400.00683.8913,083.89
22,400.00874.1016,357.99
32,400.001,076.0419,834.03
42,400.001,290.4323,524.46
52,400.001,518.0527,442.51
62,400.001,759.7131,602.21
72,400.002,016.2736,018.48
82,400.002,288.6540,707.14
92,400.002,577.8445,684.97
102,400.002,884.8650,969.84

How it works

Compound interest means you earn interest on your interest. Each time interest is added, the next round is worked out on the bigger balance, so growth speeds up over time.

The more often interest is added, the more you earn at the same yearly rate. The effective yearly rate row shows what the rate really works out to once compounding is included.

Monthly deposits are added at the end of each month and start earning from the next month. The table shows how much you added, how much interest you earned and the balance at the end of each year.

A = P × (1 + r/n)^(n × t)

P = starting amount, r = yearly rate as a decimal,
n = times interest is added per year, t = years

Worked example

10,000 at 6% a year, with interest added once a year, becomes 10,000 × 1.06¹⁰ = 17,908.48 after 10 years.

With interest added every month instead, the same money grows to 18,193.97, because the effective yearly rate rises to 6.168%.

Good to know

  • The rate is treated as fixed for the whole period. Real savings and investment returns usually change over time.
  • Tax on interest and account fees are not included. Both can make a real difference over many years.
  • Past returns do not predict future returns. This is a planning estimate, not financial advice.

Questions people ask

What is compound interest?

It is interest calculated on your money plus the interest it has already earned. Over long periods it grows much faster than simple interest, which is only paid on the original amount.

Does compounding monthly make a big difference?

It helps a little. At 6% a year, monthly compounding works out to about 6.17% a year. The bigger effects come from the rate, the number of years and regular deposits.

How long does it take to double my money?

A quick rule is 72 divided by the yearly rate. At 6% that is about 12 years. You can check it here by entering 12 years with no monthly deposits.

Is my information stored?

No. Everything is calculated in your browser and nothing you type is sent or saved.

Formulas and text last checked on 29 September 2026. Everything is calculated in your browser, so nothing you enter is sent or stored. Spotted a mistake? Tell us and we will fix it.