See how compound interest grows your money over time. Enter your initial investment, monthly contributions, and return rate. Interactive chart and free PDF export.
A compound interest calculator shows how an initial investment grows over time when interest is earned not only on the principal but also on previously accumulated interest. By entering your starting amount, contribution schedule, interest rate, and time horizon, you can see the total balance and interest earned at any future date.
124.179,03 €
Future Value
52.800,00 €
Total Contributions
71.379,03 €
Total Interest Earned
Last updated:
Compound Interest Calculator
Compound interest is one of the most powerful concepts in finance. Unlike simple interest, compound interest is calculated on both the principal and the accumulated interest from previous periods. This creates an exponential growth effect that Einstein reportedly called “the eighth wonder of the world.”
Our free calculator lets you visualize exactly how your money grows over time. Enter your initial investment, monthly contributions, expected return rate, and time horizon to see a detailed year-by-year breakdown of wealth accumulation.
How It Works
The basic formula is: A = P(1 + r/n)^(nt), where A is the final amount, P is the principal, r is the annual rate, n is the compounding frequency, and t is time in years. Our calculator uses monthly compounding (n=12), the standard for most financial products.
Investing €5,000 initially at 7% for 20 years grows to about €19,348. But if you also add €200 per month, the total grows to over €123,000 — monthly contributions and their compound interest account for more than 80% of the final value.
Rule of 72
Divide 72 by your annual interest rate to estimate how long it takes to double your money. At 6% — 12 years, at 8% — about 9 years, at 10% — roughly 7.2 years.
Historical average returns: stock market index funds 7–10%, bond funds 3–5%, savings accounts 1–3%. For long-term planning, use a conservative real return of 4–5% after inflation.
Time Is Key
An investor who starts at age 25 with €200/month at 7% will have approximately €525,000 by age 65. Someone who starts at 35 with the same amount will only have about €244,000 — starting just 10 years earlier more than doubles the result.
Weighing whether to invest or buy a home first? Our rent vs buy calculator helps you compare the long-term costs. For those managing debt, our loan calculator shows the full repayment picture.
Contribution Timing
Contributing at the start of the month rather than the end gives your money slightly more time to earn interest each period, which compounds into a measurably larger balance over many years — though the difference is usually small compared to the effect of contributing consistently at all.
More important than timing within the month is contribution frequency and consistency: an investor who contributes automatically every month for 20 years will almost always outperform one who contributes larger amounts sporadically, even if the sporadic contributor's total invested amount is similar, because missed periods mean missed compounding.
Key Principles
Annual compounding
On €10,000 at 6% for 10 years → €17,908.
Quarterly compounding
Same conditions → €18,061. Slightly better.
Monthly compounding
The standard for banking products → €18,194.
Daily compounding
Maximum effect → €18,221. Modest gain over monthly.
Real vs nominal returns
At 7% nominal and 2.5% inflation, real purchasing power grows ~4.4% annually.
Reinvest dividends
Dividend reinvestment supercharges the compounding effect over the long term.
Compound interest is interest calculated on both the initial principal and the accumulated interest from previous periods. Unlike simple interest, which is calculated only on the principal, compound interest causes your money to grow exponentially over time — often called 'interest on interest'.
Interest can be compounded annually, semi-annually, quarterly, monthly, or even daily. Our calculator uses monthly compounding, which is the most common method used by banks and financial institutions. More frequent compounding results in slightly higher returns.
Regular monthly contributions dramatically accelerate wealth building because each contribution starts earning compound interest immediately. Over long periods, the interest earned on your contributions can exceed the contributions themselves, creating a snowball effect.
The Rule of 72 is a quick way to estimate how long it takes to double your money. Divide 72 by the annual interest rate. For example, at 6% interest, your money doubles in approximately 72/6 = 12 years.
Historical stock market returns average 7-10% annually before inflation (5-7% after inflation). Savings accounts typically offer 1-3%. Bond funds average 3-5%. Use a conservative estimate (5-7%) for long-term planning to account for market volatility.
Contributing at the start of the month gives your money slightly more time to earn interest that period, resulting in a marginally larger balance over many years. The effect is small compared to the impact of contributing consistently every month without interruption.
A lump sum invested immediately has more total time in the market to compound, which historically outperforms monthly contributions (dollar-cost averaging) in a rising market. However, monthly contributions reduce the risk of investing a large sum right before a downturn and fit realistic saving patterns for most people who don't have a lump sum available.