Compound interest calculator.
Enter what you set aside each month and see what it grows into over the years — interest earning interest.
Future value
After 20 years you'd have ~€69,306 — €33,306 of it earned by interest, not by you.
years
Starting amount
Monthly contribution
Yearly return
Years
Assumes a constant yearly return. Past performance doesn't guarantee future results.
Method
How does compound interest work?
Compound interest means returns are earned not just by the money you put in, but also by the interest you've already earned. At first the difference looks tiny, but over the years this “interest on interest” effect becomes the biggest part of the pot. That's why time matters more than the amount — starting early with a small contribution usually beats starting late with a big one. The calculation assumes a constant yearly return with monthly compounding; real investments fluctuate, and past performance doesn't guarantee future results.
Last reviewed: 25 August 2026
In the app your debts, budget and savings already live in one place — the calculators fill themselves in.
Questions
Frequently asked questions.
What is compound interest in plain words?
It's interest that earns interest: returns are paid not only on the money you put in, but also on what you've already earned. That's why a pot grows faster and faster the longer it stays untouched.
What yearly return should I use?
Broadly diversified stock index funds have historically returned around 5–8% a year over the long run, but no year is guaranteed. Use 4–5% for a conservative view, 7–8% for an optimistic one — and compare both.
Is this investment advice?
No — it's an educational tool doing the math at a constant yearly return. Real investments fluctuate, and past performance doesn't guarantee future results.
Why start early, even with a small amount?
Time is the main ingredient of compounding: €50 a month for 30 years usually beats €150 a month for 10, because the interest has more time to earn interest. Drag the years slider and see for yourself.