Compound interest
How much your savings grow with regular contributions
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What is Compound interest?
Compound interest means your interest earns more interest. With this calculator you can see how much money you'll have if you invest an initial amount and add a sum every month.
A chart shows, year by year, how much is money you put in and how much is interest, so you can see the effect of time on your savings.
How to use it
- Enter the initial amount and the monthly contribution.
- Enter the expected annual interest rate.
- Choose the number of years with the slider, up to 60.
- Select the compounding frequency: annually, semi-annually, quarterly, monthly or daily.
- Check the total, the interest earned and the chart; hover over each bar to see the details.
Advantages
- Includes regular contributions, not just the initial amount.
- Shows the equivalent effective annual rate (APY) for the compounding frequency.
- Chart and table by year with contributions and interest.
- Free, no sign-up and no ads.
Technical details
The simulation runs month by month. The nominal annual rate i, compounded m times a year, is converted to an equivalent monthly rate rm = (1 + i/m)^(m/12) − 1, and each month the balance becomes balance × (1 + rm) + contribution, with contributions at the end of each month. Without contributions, the result matches the classic formula C × (1 + i/m)^(m·t). The effective annual rate shown is (1 + i/m)^m − 1. Negative amounts are treated as zero and the horizon goes up to 60 years. It doesn't take inflation, fees or taxes on gains into account.
Frequently asked questions
What is compound interest?
It's interest calculated on the principal and also on the interest already accumulated. That way money grows faster and faster over time.
What is the compound interest formula?
Final amount = C × (1 + i/m)^(m·t), where C is the principal, i the annual rate, m the compounding periods per year and t the years. With monthly contributions, each contribution is added with its own growth.
How much will I have if I save €200 a month at 5%?
With €10,000 to start, €200 a month and 5% a year compounded monthly, after 20 years you'll have about €109,000, of which €58,000 are contributions.
What's the difference between monthly and annual compounding?
With monthly compounding, interest is added every month and starts earning more interest sooner, so the effective annual rate is slightly higher than the nominal rate.
Does it include inflation or taxes?
No. It shows nominal growth before taxes and without adjusting for inflation.
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