Compound Interest Calculator
Discover the power of compound growth using real historical returns of the S&P 500, MSCI World, Nasdaq 100, and more. Set your initial investment, contributions, and time horizon.
~10.7% annualized (1957–2026)
Portfolio Value in 20 Years
Total Invested
$130,000
Total Gains
+$370,222
Return on Capital
+285%
Annual Rate
10.7%
Growth Trajectory
⚠️ Past returns do not guarantee future results. This calculator uses nominal returns before taxes and inflation. Educational purposes only — not financial advice.
Why Time in the Market Always Beats Timing the Market
Compound interest works because returns generate their own returns. A $10,000 investment earning 10% annually becomes $11,000 after year one. In year two, that $11,000 earns 10% — giving you $12,100, not just $12,000. The extra $100 is your compounding at work.
The longer your time horizon, the more dramatic this effect becomes. Investing $500/month from age 25 to 65 at a 10% annual return produces roughly $3.2 million. Starting at 35 instead produces only $1.1 million — three times less, despite only losing 10 years. This is the single most powerful argument for starting immediately.
The S&P 500's historical average of ~10.7% per year (including dividends) is the most cited benchmark for long-term investors. The MSCI World provides geographic diversification with slightly lower but still impressive returns. Index funds and ETFs make accessing these returns easier than ever, with expense ratios below 0.10% in many cases.