Compound interest calculator
See what your money grows to, or work backwards from a goal: the monthly saving, the time or the rate it takes.
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Your savings grow to €817,658 in 21 years.
You pay in €339,000; interest adds €478,658, 59% of the end amount.
- End amount
- €817,658
- Paid in
- €339,000
- Interest earned
- €478,658
- Money doubles every
- 10.2 years
- Paid in
- Interest
What if… end amount
See the figures
| Year | Paid in | Interest | Balance |
|---|---|---|---|
| Year 1 | €39,000 | €2,226 | €41,226 |
| Year 2 | €54,000 | €5,697 | €59,697 |
| Year 3 | €69,000 | €10,503 | €79,503 |
| Year 4 | €84,000 | €16,741 | €100,741 |
| Year 5 | €99,000 | €24,514 | €123,514 |
| Year 6 | €114,000 | €33,934 | €147,934 |
| Year 7 | €129,000 | €45,119 | €174,119 |
| Year 8 | €144,000 | €58,196 | €202,196 |
| Year 9 | €159,000 | €73,304 | €232,304 |
| Year 10 | €174,000 | €90,588 | €264,588 |
| Year 11 | €189,000 | €110,206 | €299,206 |
| Year 12 | €204,000 | €132,326 | €336,326 |
| Year 13 | €219,000 | €157,130 | €376,130 |
| Year 14 | €234,000 | €184,811 | €418,811 |
| Year 15 | €249,000 | €215,578 | €464,578 |
| Year 16 | €264,000 | €249,653 | €513,653 |
| Year 17 | €279,000 | €287,275 | €566,275 |
| Year 18 | €294,000 | €328,702 | €622,702 |
| Year 19 | €309,000 | €374,208 | €683,208 |
| Year 20 | €324,000 | €424,088 | €748,088 |
| Year 21 | €339,000 | €478,658 | €817,658 |
Next step
How the calculator works
Compound interest means interest earns interest. For a single deposit it is one formula:
End amount = Start × (1 + r)n
with the yearly rate r as a decimal and n years. €10,000 at 5 % becomes €16,289 after 10 years. Simple interest would add only €5,000; the rest is interest on interest.
With monthly savings the calculator works month by month:
- Each month’s saving arrives at the end of the month.
- With monthly compounding, a twelfth of the yearly rate is credited every month and earns interest straight away.
- With yearly compounding, interest is credited at the end of the year. Until then each deposit earns simple interest for the months it was in the account, as many banks calculate it.
- With a yearly increase, the monthly saving rises by that percentage at the start of each new year.
For “Monthly saving”, “Time needed” and “Interest rate” the calculator turns the question around and finds the value that reaches your target exactly.
Example: Lena and Jonas in Berlin
Lena and Jonas, both 34, have €24,000 saved and put away €1,250 a month. At 7% a year their money grows to €817,658 in 21 years. They paid in €339,000; the other €478,658 is compound interest.
The return is the assumption that matters most. One percentage point more or less moves the result by six figures over two decades. Try it with the “What if” buttons above.
Future money or today’s money?
An amount in 20 years buys less than the same amount today. At 2 % inflation, prices are about 49 % higher after 20 years. Under “More assumptions”, switch on today’s money to compare results with today’s prices, or see the effect in the inflation calculator.
What it can’t see
It uses one fixed rate. Shares deliver their return in good and bad years, not evenly, and for a plan it matters when the bad years come. It does not deduct tax or fund costs; the ETF savings plan calculator does. And it doesn’t know about the child, the home or the career break ahead. That is what Zenarios puts together: saving, tax, pensions and your plans in one forecast.
Common questions
How is compound interest calculated?
For a lump sum, end amount = start × (1 + rate)^years. €10,000 at 5 % becomes €16,289 after 10 years. With monthly deposits each payment compounds from the month it arrives; this calculator works it out month by month.
How much will 10,000 grow to in 10 years?
With interest credited yearly, 10,000 becomes 13,439 at 3 %, 16,289 at 5 % and 19,672 at 7 % after 10 years, before inflation and tax.
How long does it take to become a millionaire?
Choose “Time needed” above and enter 1,000,000 as the target. Starting from zero with 500 a month at 7 %, it takes about 36½ years; with 1,000 a month about 27½. A million then is worth much less in today's money; switch on the today's-money view to see how much.
What's the difference between monthly and yearly compounding?
Monthly compounding credits a twelfth of the yearly rate every month, and that interest earns interest straight away. Yearly compounding (common for savings accounts) pays simple interest on deposits until the year ends and credits it then. Monthly gives slightly more at the same rate.
Does it include tax?
No. Interest and gains are taxable in most countries; in Germany above the €1,000 saver's allowance at about 26.4 %. For ETFs with German tax rules, use the ETF savings plan calculator.