Compound Interest Calculator
Calculate compound interest with monthly contributions and a year-by-year breakdown. See total interest earned and projected balance over any horizon.
%
Final balance
170,619.05
Total contributions
70,000.00
Interest earned
100,619.05
Year-by-year breakdown
| Year | Contributions | Interest | Balance |
|---|---|---|---|
| 1 | 13,000.00 | 821.05 | 13,821.05 |
| 2 | 16,000.00 | 1,918.32 | 17,918.32 |
| 3 | 19,000.00 | 3,311.78 | 22,311.78 |
| 4 | 22,000.00 | 5,022.85 | 27,022.85 |
| 5 | 25,000.00 | 7,074.48 | 32,074.48 |
| 6 | 28,000.00 | 9,491.29 | 37,491.29 |
| 7 | 31,000.00 | 12,299.69 | 43,299.69 |
| 8 | 34,000.00 | 15,527.97 | 49,527.97 |
| 9 | 37,000.00 | 19,206.50 | 56,206.50 |
| 10 | 40,000.00 | 23,367.82 | 63,367.82 |
| 11 | 43,000.00 | 28,046.83 | 71,046.83 |
| 12 | 46,000.00 | 33,280.95 | 79,280.95 |
| 13 | 49,000.00 | 39,110.33 | 88,110.33 |
| 14 | 52,000.00 | 45,577.98 | 97,577.98 |
| 15 | 55,000.00 | 52,730.04 | 107,730.04 |
| 16 | 58,000.00 | 60,616.00 | 118,616.00 |
| 17 | 61,000.00 | 69,288.91 | 130,288.91 |
| 18 | 64,000.00 | 78,805.65 | 142,805.65 |
| 19 | 67,000.00 | 89,227.23 | 156,227.23 |
| 20 | 70,000.00 | 100,619.05 | 170,619.05 |
Compound interest is interest you earn on the interest you've already earned. Over long horizons it's the single most powerful force in personal finance: a modest monthly contribution at a modest rate compounds into a meaningfully larger number than the sum of those contributions on their own.
This calculator projects the future value of a starting balance plus optional monthly contributions at a given rate, with the choice of compounding frequency. The year-by-year table shows how much of the final balance is your money in (contributions) versus the interest the account did for you.
How to use
- Enter your starting balance and the monthly amount you'll add (set either to zero if not applicable).
- Enter the annual interest rate and the time horizon in years.
- Pick a compounding frequency. Most savings products compound monthly; some bonds compound annually; some money-market accounts compound daily.
- Read the final balance and the year-by-year breakdown to see how the curve grows.
Frequently asked questions
- How is compound interest different from simple interest?
- Simple interest is calculated only on the original principal each period. Compound interest is calculated on the principal plus all previously accrued interest, so each period's interest grows the base for the next period. Over long horizons the difference is dramatic.
- Does compounding frequency really matter?
- Less than people think, at least at moderate rates. The difference between annual and monthly compounding at 7% over 30 years is small (a percent or two of total balance). The big lever is rate × time, not frequency.
- What rate should I use?
- For long-term stock-market investments, 6–8% (after inflation) is a common assumption based on historical returns. For savings accounts and CDs, use the actual posted rate. For inflation-adjusted projections, subtract your expected inflation rate from a nominal expected return.
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