Enter a starting balance, rate, compounding frequency, contribution amount, and time horizon. The calculator shows the modeled balance and a year-by-year view.
At 7% annual interest with monthly compounding and no contributions, the modeled balance after 20 years is $40,387. Total contributions are $10,000 and modeled interest is $30,387.
Inputs: $10,000 starting amount, no monthly contribution, 7% annual rate compounded monthly, 20 years.
Inputs changed: press Calculate to see the result.
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| Year | Paid in | Interest that year | Total interest | Balance |
|---|---|---|---|---|
| 1 | $10,000 | $723 | $723 | $10,723 |
| 2 | $10,000 | $775 | $1,498 | $11,498 |
| 3 | $10,000 | $831 | $2,329 | $12,329 |
| 4 | $10,000 | $891 | $3,221 | $13,221 |
| 5 | $10,000 | $956 | $4,176 | $14,176 |
| 6 | $10,000 | $1,025 | $5,201 | $15,201 |
| 7 | $10,000 | $1,099 | $6,300 | $16,300 |
| 8 | $10,000 | $1,178 | $7,478 | $17,478 |
| 9 | $10,000 | $1,264 | $8,742 | $18,742 |
| 10 | $10,000 | $1,355 | $10,097 | $20,097 |
| 11 | $10,000 | $1,453 | $11,549 | $21,549 |
| 12 | $10,000 | $1,558 | $13,107 | $23,107 |
| 13 | $10,000 | $1,670 | $14,778 | $24,778 |
| 14 | $10,000 | $1,791 | $16,569 | $26,569 |
| 15 | $10,000 | $1,921 | $18,489 | $28,489 |
| 16 | $10,000 | $2,060 | $20,549 | $30,549 |
| 17 | $10,000 | $2,208 | $22,757 | $32,757 |
| 18 | $10,000 | $2,368 | $25,125 | $35,125 |
| 19 | $10,000 | $2,539 | $27,665 | $37,665 |
| 20 | $10,000 | $2,723 | $30,387 | $40,387 |
Interest is added to the balance, and later periods can earn interest on that larger balance. Time, rate, and contribution timing all matter.
On these inputs the balance earns $723 of interest in year 1 and $2,723 in year 20. The year-by-year table above shows every year in between.
Each monthly contribution is added at the end of its month and starts earning from the following month, so the money put in first spends the longest growing.
How often interest is added matters less than the rate or the time. The same inputs at different compounding frequencies:
| Compounding | Effective annual rate | Modeled balance |
|---|---|---|
| Annual | 7.00% | $38,697 |
| Monthly (your inputs) | 7.23% | $40,387 |
| Daily | 7.25% | $40,547 |
This is a fixed-rate calculation, not a forecast of an investment return. The same rate applies in every period, and taxes, fees and inflation are not part of the result.
$10,000 at 7% compounded monthly has a modeled balance of $40,387 after 20 years, including $30,387 of modeled interest. The result uses the inputs shown and the method described on this page. It excludes taxes, fees and inflation, and it is a fixed-rate calculation, not a forecast. Reproduce the calculation here: https://smartfin.fyi/compound-interest-calculator.html?principal=10000&contribution=0&rate=7&frequency=12&years=20.
For a single lump sum under periodic compounding, the formula is A = P(1 + r/n)nt: P is the starting amount, r the annual rate as a decimal, n the number of times interest is added a year and t the number of years. Here that is $10,000 × (1 + 7% ÷ 12)12 × 20 = $40,387.
The yearly rate once compounding is counted: (1 + r/n)n − 1. 7% compounded monthly is an effective 7.23% a year.
No. The $40,387 is the arithmetic of a fixed rate: no tax on interest, no account or fund fees, and no adjustment for inflation. The Inflation Calculator shows what an amount is worth in today’s money.