Compound Interest Calculator
See how a starting balance and regular monthly deposits grow when the interest keeps earning interest, with any compounding frequency and, if you like, in today's dollars.
Configure Your Savings
Results
$10,000 + $500/mo · 7% · 20 years
$292,465
estimated balance after 20 years
Total Contributions
$130,000
Interest Earned
+$162,465
Money Doubles Every
10.2 yrs
Balance Over Time
Show the chart data as a table
| Period | Contributions | Balance |
|---|---|---|
| Year 1 | $16,000 | $16,890 |
| Year 2 | $22,000 | $24,263 |
| Year 3 | $28,000 | $32,151 |
| Year 4 | $34,000 | $40,592 |
| Year 5 | $40,000 | $49,623 |
| Year 6 | $46,000 | $59,287 |
| Year 7 | $52,000 | $69,627 |
| Year 8 | $58,000 | $80,692 |
| Year 9 | $64,000 | $92,530 |
| Year 10 | $70,000 | $105,197 |
| Year 11 | $76,000 | $118,751 |
| Year 12 | $82,000 | $133,254 |
| Year 13 | $88,000 | $148,772 |
| Year 14 | $94,000 | $165,376 |
| Year 15 | $100,000 | $183,143 |
| Year 16 | $106,000 | $202,153 |
| Year 17 | $112,000 | $222,494 |
| Year 18 | $118,000 | $244,258 |
| Year 19 | $124,000 | $267,547 |
| Year 20 | $130,000 | $292,465 |
Frequently Asked Questions
What is compound interest?
Compound interest is interest earned on earlier interest, not just on the money you put in. Each year's growth is added to the balance, so the next year grows a larger amount. Saving $500 a month for 30 years at 7% a year adds up to $180,000 of contributions, but grows to about $584,726: $404,726 of it is interest.
How often is interest compounded, and does it matter?
Savings accounts usually compound daily or monthly; investment returns are usually quoted per year. More frequent compounding helps a little at the same quoted rate: $10,000 at 7% for 20 years grows to $38,697 compounded annually, $40,387 monthly and $40,547 daily. The rate and the time matter far more than the frequency.
What interest rate should I use?
For stocks over the long run, 7% a year is a common cautious figure. The S&P 500 (SPY, dividends reinvested) returned 10.8% a year from Jan 1993 to Oct 2026, but with large swings along the way. For a savings account or CD, use its current rate.
What is the Rule of 72?
A shortcut for how long money takes to double: divide 72 by the yearly rate. At 7%, 72 ÷ 7 ≈ 10.3 years; the exact figure is 10.2 years. The calculator shows the exact doubling time for your rate.
What does 'today's dollars' mean?
Prices rise over time, so a dollar in 30 years buys less than a dollar today. Ticking 'Show in today's dollars' divides each future amount by the inflation since today, so the balance shows what it would buy now. U.S. inflation has averaged about 3% a year over the long run.
See our Methodology page for how the figures are calculated, or all calculators. For education only, not investment, tax or legal advice. Past performance does not guarantee future results.