Compound Interest Playground
Slide the numbers and watch small, regular amounts snowball. Then see what it costs to start five or ten years later.
Your numbers
You could have
$300,276
3.0× what you put in
Money you put in
$100,000
Growth on top
$200,276
At 7.0% a year, money doubles roughly every 10.3 years.
What waiting costs
Same monthly amount, same end date — only the start moves.
An illustration, not a forecast. Assumes a steady return compounded monthly, contributions at month end, and no taxes, fees or inflation. Real markets do not move in straight lines.
What the market actually returned
Average yearly return of the S&P 500 in each decade since 1920. Two of the eleven lost money. The other nine paid for them.
- +18.0%
- 1920s
- Roaring Twenties bull market
- -0.9%
- 1930s
- Great Depression
- +9.0%
- 1940s
- WWII and postwar boom
- +19.4%
- 1950s
- Post-war expansion and consumer boom
- +7.8%
- 1960s
- Space Race, Vietnam War spending
- +5.9%
- 1970s
- Oil crisis and stagflation
- +17.3%
- 1980s
- Reaganomics and market deregulation
- +18.1%
- 1990s
- Dot-com and technology boom
- -0.9%
- 2000s
- Dot-com bust and financial crisis
- +13.5%
- 2010s
- Longest bull market in history
- +7.0%
- 2020s
- Pandemic shock and AI-driven rebound
Best decade
1950s +19.4%
Post-war expansion and consumer boom
Worst decade
1930s -0.9%
Great Depression
Decade averages, price return excluding dividends. Past performance does not guarantee future results.