Compound Interest Calculator
Discover the power of compound interest with our free calculator.
100% in-browser ยท no data sent
See exactly how your investments will grow over time with regular contributions. Visualize your financial future with detailed year-by-year breakdowns and scenario comparisons. Perfect for retirement planning, college savings, and long-term investment goals.
Embed This Tool
Add this tool to your website with customizable styling
How to Use
- 1 Enter starting amount โ Input your initial investment (principal). This is the money you're starting with today.
- 2 Add regular contributions โ Include monthly, quarterly, or annual contributions. Even small amounts add up significantly over time due to compound interest.
- 3 Set interest rate โ Enter your expected annual return. Conservative: 4-6%, Moderate: 6-8%, Aggressive: 8-12%. Historical S&P 500 average is about 10%.
- 4 Choose time period โ Select how many years you plan to invest. The longer the period, the more dramatic the compound growth.
- 5 Review results โ See your future value, total interest earned, and return on investment. The breakdown shows how much came from contributions vs compound interest.
- 6 Compare scenarios โ Try different combinations to see how changing contributions, interest rates, or time periods impacts your results.
Frequently Asked Questions
What is compound interest?
Compound interest is 'interest on interest' - you earn returns not just on your initial investment, but also on your accumulated earnings. For example: If you invest $1,000 at 10% annual return, after year 1 you have $1,100. In year 2, you earn 10% on $1,100 (not just the original $1,000), giving you $1,210.
How much does compound interest really matter?
It matters enormously over long time periods. $10,000 invested at 8% annual return becomes $46,610 after 20 years with compound interest, but only $26,000 with simple interest. That's $20,610 MORE just from compounding!
Why is starting early so important?
Time is the most powerful factor. If you invest $200/month starting at age 25 until 65 (40 years) at 8% return, you'll have $622,000. Start at age 35 instead (30 years), and you'll only have $298,000 - that's $324,000 less despite only a 10-year difference!
What's a realistic interest rate to expect?
It depends on your investment type: High-yield savings: 4-5%, Bonds: 3-6%, Balanced mutual funds: 6-8%, Stock market (S&P 500 historical average): ~10%, Individual stocks: Highly variable. Higher returns usually mean higher risk.
How often should interest compound?
More frequent compounding is better, but the difference is relatively small. At 8% over 20 years on $10,000: Annually: $46,610, Monthly: $47,931, Daily: $48,051. Most savings accounts compound daily or monthly.
How does inflation affect my returns?
Inflation erodes purchasing power. If you earn 8% but inflation is 3%, your 'real return' is only about 5%. Enable our inflation adjustment to see real vs nominal returns.