Compound Interest Calculator: the strongest force in building wealth
Enter a lump-sum investment, an expected return, and a time horizon — and see how much of it is pure compound interest.
Simplified model with a fixed return, not investment advice. Actual returns fluctuate.
After 20 years you'd have roughly €38,697.00.
Assuming a return of 7% per year, before taxes and fees.
Final capital
€38,697.00
Contributed
€10,000.00
Interest earned
€28,697.00
How it works
Understanding compound interest
Why a lump sum grows so strongly over time.
The formula behind it
Capital × (1 + return)^years — every year, not just the starting capital but also the gains already earned get compounded.
Lump sum vs. savings plan
With a lump sum, the entire capital works from day one — the savings plan calculator shows the effect of adding a monthly contribution on top.
The time factor
Compounding accelerates exponentially over time — the last years of a long horizon often contribute the most.
Frequently asked
Questions about the compound interest calculator
Compound interest means gains aren't paid out but reinvested and earn further gains themselves — so capital grows faster over time than with simple interest.
Both use the same underlying math — this calculator emphasizes a lump sum, the savings plan calculator a recurring monthly contribution. You can adjust either figure in both.
The calculator assumes a constant annual return and doesn't account for taxes, fees, or market swings — it's a rough guide, not financial advice.
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