Compound Interest Calculator - Project the growth of your savings
Estimate at a constant rate, before taxes and fees. Contributions are made at the end of each period.
How to use this calculator?
1. Enter your starting capital (0 if you start from scratch)
2. Enter the amount of your regular contributions and how often you make them
3. Enter the annual interest rate, the duration and the compounding frequency
4. Read the final capital, the interest earned and the year-by-year table
Quick answer
How do you calculate compound interest?
Use the formula A = P × (1 + r)^n, where P is the starting capital, r the annual rate and n the number of years: each year the interest is added to the capital and earns interest in turn. Example: €10,000 invested at 4% a year for 10 years grows to €14,802.44, which is €4,802.44 of interest.
| Years | Capital (€10,000 at 4%) | Interest earned |
|---|---|---|
| 1 | €10,400.00 | €400.00 |
| 5 | €12,166.53 | €2,166.53 |
| 10 | €14,802.44 | €4,802.44 |
| 20 | €21,911.23 | €11,911.23 |
| 30 | €32,433.98 | €22,433.98 |
About the Compound interest calculator
What is it?
The compound interest calculator estimates the future value of your savings from a starting capital, regular contributions (monthly or yearly), an annual interest rate and a duration. It shows the final capital, the total paid in, the interest earned and the year-by-year growth.
Why use it?
With compound interest, the interest you earn starts earning interest too, so the gap with a simple sum of contributions widens over time. Running a few scenarios helps you see the effect of duration, rate and regular saving before choosing an investment.
How does it work?
Without contributions, and when compounding matches the period, the formula is A = P × (1 + r/n)^(n × t), where r is the annual rate, n the number of compounding periods per year and t the duration in years. To combine contributions and compounding at different frequencies, the calculation is simulated month by month using the equivalent monthly rate (1 + r/n)^(n/12) - 1. Each contribution is added at the end of its period (end of month, or end of year for yearly contributions), and the interest earned is the final capital minus the total paid in.
Usage tips
- Starting early often matters more than contributing a lot: time amplifies compounding
- Compare rates net of fees: a few tenths of a percent in yearly fees noticeably reduce the final capital over long periods
- Taxes are not included, so the amount you actually receive may be lower
- A constant rate over decades is an assumption: try several rates to get a range
- Use the share button to send or bookmark your simulation
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