Compound interest calculator
Find out how much your money could grow if you reinvest the returns and add a fixed amount every month.
Compound interest calculator: what it is and how it works
Compound interest means reinvesting the interest your money earns so that it, in turn, earns more interest. Unlike simple interest, growth is exponential rather than linear: the longer you wait, the faster your balance grows. That is why time is a saver’s best friend.
This calculator combines an initial amount with regular monthly contributions and applies each month the rate equivalent to the annual return you enter. It shows your final balance, how much you put in and how much comes from interest, along with a year-by-year table. Remember that past returns do not guarantee future ones.
How to use it
- Enter your starting amount and how much you will add each month.
- Enter the expected annual return and the number of years.
- See the final balance and how interest builds up each year.
FV = P × (1 + r)^t + A × ((1 + i)^n − 1) ÷ i · i = (1 + r)^(1/12) − 1Worked example
Starting with €10,000, adding €200 a month and earning 5 % a year for 20 years, you contribute €58,000 and end up with €107,693.87 — €49,693.87 of it is interest.
Frequently asked questions
What is the difference between simple and compound interest?
Simple interest is always calculated on the original amount. Compound interest is added to the balance and earns interest itself, so growth speeds up over time.
What is the rule of 72?
A shortcut for how long money takes to double: divide 72 by the annual return. At 7 %, about 10 years; at 4 %, about 18.
Are taxes and inflation included?
No. The calculation uses the return you enter. For a more realistic estimate, enter a return net of taxes, fees and inflation.
How often is interest compounded?
Monthly, using the rate equivalent to the effective annual return you enter, so a full year yields exactly that return.