Project how savings or an ETF plan grow with compound interest. Set a starting amount, monthly contribution, return and duration, and watch the balance grow year by year.
How to use the Compound Interest
Enter your starting amount, monthly contribution, expected return and number of years.
See the final balance split into what you invested and the interest earned.
Use the chart to watch the balance grow year by year.
This compound interest calculator shows how a one-off starting amount plus regular monthly contributions can grow over time at a constant annual return. It separates the total you put in from the interest earned, so the effect of compounding is easy to see.
Contributions are added at the start of each month and the balance is compounded monthly, which matches how most savings and ETF plans actually work, and a year-by-year chart shows the balance climbing.
Compound interest is interest on your interest. Each period, the return is calculated on your contributions plus all the gains so far, so the balance grows faster and faster. Over long horizons this compounding, not the contributions, drives most of the final amount.
A rough mental check is the rule of 72: dividing 72 by the annual return gives the years for money to double. At 7 percent, that is about ten years, which is why starting early matters so much.
Returns are assumptions, not guarantees. A broad global stock ETF has historically averaged roughly 6 to 8 percent per year before inflation over long periods, but any given stretch can be very different, including negative.
The projection is before taxes, fees and inflation, so treat the result as a gross estimate and leave a margin for those. Everything is calculated in your browser.
Frequently asked questions
Compound interest is interest earned on both your contributions and previously earned interest. Over long periods this compounding drives most of the growth.
Contributions are added at the start of each month and the balance is compounded monthly, which matches how many savings plans and ETF savings plans work.
Returns are never guaranteed. A broad global stock ETF has historically averaged roughly 6 to 8 percent per year before inflation over long horizons, but any given period can differ a lot.
No. The projection is before taxes, fees and inflation. Treat the result as a gross estimate and plan a margin for those factors.
A quick estimate: divide 72 by the annual return to get the years for your money to double. At 6 percent that is about 12 years, at 8 percent about 9.
This tool is for general information only and is not financial, tax, or legal advice. Results are estimates that depend on your situation and current rules, so check the official source or a qualified professional before you act.
Embed this tool
Add this tool to your own website. Copy the snippet below; it stays up to date automatically.
<iframe src="https://monu.tools/embed/en/zinsrechner" width="100%" height="640" style="border:1px solid #e5e5e5;border-radius:12px;max-width:680px" loading="lazy" title="Monu Tools"></iframe>Related tools
Estimate your German statutory pension from your salary and contribution years using the official pension formula, including early or later retirement and health and care insurance.
Calculate the monthly payment, total interest and effective APR for an annuity loan or credit. Includes an optional fee and a year-by-year repayment chart.
Estimate the tax on a German severance payment with the one-fifth rule (§34 EStG), and see how much that rule saves compared with normal taxation.
Estimate German statutory sick pay (Krankengeld): 70 % of your gross, capped at 90 % of net and the contribution ceiling, minus social contributions.