Compound interest calculator
Start with any balance, add a monthly contribution, pick a rate — and watch what time does to money. This is the math behind every savings account and retirement plan.
Projected balance
Assumes monthly compounding and a constant return. Real returns vary year to year, and investing involves risk of loss. Doesn't account for taxes, fees, or inflation.
The one thing to notice
Run the same numbers at 10 vs. 20 vs. 30 years. The growth isn't linear — it accelerates, because each year's earnings start earning their own returns. That's why starting earlier usually matters more than starting bigger.
Picking a realistic rate
For money in a high-yield savings account, use the APY your bank actually pays today. For long-term investing, historical U.S. stock-market averages are often cited around 7–10% annually before inflation — but past performance doesn't guarantee future results, and any single decade can look very different.