Why this matters
$500/month is about $6,000/year. Over 20 years you contribute $110,000 total ($10k + $120k in deposits), but compound interest pushes the balance well beyond that.
The key formula is A = P × (1 + r/n)n·t, where time (t) sits in the exponent. That's why starting early — even with smaller amounts — often beats saving larger amounts later.
Try different scenarios
Adjust the inputs above to see how changing the rate, monthly contribution, or time horizon affects your outcome. For goal-based planning, try the savings goal calculator. To see investment returns against market benchmarks, try the investment calculator. Learn more in our guide to compound interest.
What to keep in mind
This calculator assumes a fixed annual return of 7%, which is useful for projections but doesn't reflect real-world volatility. Stock market returns average about 10% annually over decades, but individual years can vary from −30% to +30%. Bonds and savings accounts offer lower but more stable returns. Diversifying across asset classes helps balance risk and growth. Also note that investment gains may be subject to taxes — a tax-advantaged account like a 401(k) or IRA can help your money grow more efficiently.
- What is compound interest?
- Interest earned on both the original principal and on previously earned interest — creating exponential growth over time.
- How much will $10,000 plus $500/mo grow at 7%?
- At 7% over 20 years, your initial deposit of $10,000 with $500 monthly contributions grows significantly through compounding. Use the calculator above to see the exact projection.
- Are returns guaranteed?
- No — this calculator shows projected growth at a fixed rate. Actual investment returns vary. Savings accounts offer guaranteed but lower returns, while stocks have higher potential but more volatility.