Compound interest calculator
Enter a starting amount, an interest rate and a term and see at once what your money grows to, with interest on interest. If you add to it every month, fill that in too. Under the result you get a year-by-year table.
What you put in now. May be empty if you only save monthly.
The percentage per year, for example 3.5.
Part of a year is fine too, such as 2.5.
Optional. This amount is added at the end of every month.
Fill in the fields; the answer appears here straight away.
How it's worked out
How it works
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Enter the values
Type the numbers or the formula. Decimals may use a point or a comma. No idea? Click Fill in an example.
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Instant answer
The answer appears as you type, with the most important intermediate values.
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See the working
Under "How it's worked out" you see the steps, handy for checking your own calculation.
What is compound interest?
With compound interest you earn interest on your deposit and on the interest you earned before. That makes an amount grow faster and faster. Without deposits the formula is:
final amount = start × (1 + rate) ^ years
10,000 at 3.5% a year is, after 10 years, 10,000 × 1.035¹⁰ = 14,105.99. You have then received 4,105.99 in interest.
Adding every month
With 100 extra a month, paid in at the end of each month, the same example becomes 28,408.09: 22,000 paid in (10,000 + 120 × 100) and 6,408.09 in interest. The longer the term, the bigger the effect: 200 a month for 30 years at 4% gives 137,054.11, of which 72,000 is your own money.
Credited yearly, monthly or daily
If your bank credits interest more often, your money grows slightly faster. The tool turns this into the effective yearly return: 3.5% credited monthly is about 3.56% a year. You see that return under the result.
Good to know
Tax, fees and changing rates are not included, and returns on investments are not guaranteed. Use the result as an indication.
What a long term does
| Plan | Paid in | Result | Interest |
|---|---|---|---|
| 1,000 at 7% for 20 years | 1,000 | 3,869.68 | 2,869.68 |
| 100 a month at 5% for 40 years | 48,000 | 148,252.46 | 100,252.46 |
| 200 a month at 4% for 30 years | 72,000 | 137,054.11 | 65,054.11 |
In the second plan more than two thirds of the result is interest. The first and last years contribute very different amounts: the year-by-year table shows interest growing every year as the balance grows.
Start early
Time matters more than the amount. The same 100 a month for 40 years is worth 148,252, while 20 years would give only about 41,000 for 24,000 paid in. The interest of the early years keeps earning interest for decades.
Interest and loans
Loans use the same mathematics in reverse: the interest works against you. The loan payment calculator shows what a loan costs in total, and the percentage calculator helps with the share of interest in a payment.
Frequently asked questions
What is the difference between the nominal and the effective rate?
The nominal rate is the quoted yearly rate. The effective rate is what you actually earn in a year once the interest is credited more often than yearly. 2% credited monthly is an effective 2.018% a year, which the calculator shows.
Does it matter whether interest is credited yearly, monthly or daily?
A little. 5,000 at 2% for 5 years becomes 5,520.40 with yearly crediting and 5,525.39 with monthly crediting, a difference of about 5. The rate and the term matter far more than the frequency.
When are monthly deposits added?
At the end of each month. Deposits made at the start of the month would earn slightly more, so the result is on the cautious side.
How long does it take to double my money?
Divide 72 by the rate: at 6% about 12 years, at 3.5% about 20.6. For the exact figure and other growth rates, use the [exponential growth calculator](/en/math/exponential-growth-calculator).