Compound Interest Calculator
See how your investment grows over time through the power of compound interest. Enter your initial capital, any monthly additions, expected annual return and investment period — the calculator shows the final value and year-by-year growth.
Total invested
34 000 €
Return
58 480 €
Value in 20 years
92 480 €
172,0 % return · 2,7x initial investment
| Year | Invested | Return | Total value |
|---|---|---|---|
| 2 | 12 400 € | 1 666 € | 14 066 € |
| 4 | 14 800 € | 3 941 € | 18 741 € |
| 6 | 17 200 € | 6 917 € | 24 117 € |
| 8 | 19 600 € | 10 698 € | 30 298 € |
| 10 | 22 000 € | 15 405 € | 37 405 € |
| 12 | 24 400 € | 21 177 € | 45 577 € |
| 14 | 26 800 € | 28 172 € | 54 972 € |
| 16 | 29 200 € | 36 576 € | 65 776 € |
| 18 | 31 600 € | 46 597 € | 78 197 € |
| 20 | 34 000 € | 58 480 € | 92 480 € |
How does the calculator work?
The calculator uses monthly compounding. Returns are added to the principal each month, so the following month's return is calculated on a larger sum. This is the compound interest effect.
Value = Initial × (1 + r)^n + Monthly × [((1 + r)^n − 1) / r]
where r = annual return / 12 and n = number of months.
What return rate should I use?
The long-term historical real return of equity markets has been approximately 7–10% per year before costs and inflation. After inflation the real return is typically around 5–7%. Use a conservative estimate, for example:
- 5% — cautious estimate, accounts for costs and inflation
- 7% — historical nominal stock market return
- 10% — optimistic estimate, ignores costs or inflation
Note: The calculator is an estimate. Actual returns may differ significantly due to market fluctuations. Past performance does not guarantee future results.
The power of time – why start early?
The compound interest effect grows exponentially over time. In the early years growth feels slow, but over decades the return often exceeds the invested capital many times over.
A €10,000 lump-sum investment at 7% annual return grows to:
- 10 years → approximately €19,700
- 20 years → approximately €38,700
- 30 years → approximately €76,100
- 40 years → approximately €149,700
The impact of monthly savings
Regular monthly contributions amplify the compound effect significantly. Even a small monthly addition builds principal on which returns compound for all remaining years.
Monthly investing also spreads purchases over time, reducing the risk of investing everything at a market peak.
Read more about compound interest or explore investment strategies.