Compound Interest Calculator
These figures are nominal, before inflation. At around 3% yearly inflation, money loses roughly half its buying power over 25 years, so the real value of the final amount is lower than the headline number.
Projected growth
| Year | Invested | Value | Interest |
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What is Compound Interest Calculator
A compound interest calculator shows how money grows over time when interest is earned on both the principal and accumulated interest. Unlike simple interest, compound interest accelerates growth — the longer you invest, the faster the returns compound. This tool lets you model real investment scenarios with an initial amount, regular monthly contributions, a chosen interest rate, and a time horizon.
How to use
- Enter your initial investment amount (or 0 if starting from scratch).
- Enter the amount you plan to contribute each month.
- Set the annual interest rate — use historical averages (e.g. 7% for a diversified stock index fund).
- Choose the investment period in years and the compounding frequency.
- Review the final amount, total invested, and total interest earned. Scroll down for the year-by-year breakdown.
When to use it
Curious what steady investing really adds up to? Put in $10,000, add $500 a month at an 8% annual return for 30 years, and watch it grow past $740,000, even though only $190,000 of that came out of your pocket. The rest is compound interest doing the work for you.
Frequently asked questions
What is compound interest?
Compound interest means earning interest on your interest. Each period, the interest earned is added to your principal, so the next period you earn interest on a larger base. Over long periods this creates exponential growth.
Monthly vs annual compounding — does it matter?
Yes. Monthly compounding gives slightly better returns because interest is applied more frequently. For an 8% annual rate, monthly compounding yields about 8.3% effective annual return vs exactly 8% for annual compounding.
What interest rate should I use?
For historical planning: global diversified index funds have returned ~7-10% annually over decades. For savings accounts or fixed income, use the current rate from your bank or broker. Never assume past returns guarantee future ones.
Can I share this tool with my inputs pre-filled?
Yes. The URL updates automatically as you type. Copy it from the address bar or use the Share button — anyone who opens the link will see your exact inputs ready to go.
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