Calculate how your savings and investments could grow over time with compound interest and monthly contributions.
Compounded monthly · Deposits at month-end
After 20 years A scenario, not a forecast.
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Year 20 · Balance $300,850.72 · Invested $130,000.00
Use the arrow keys to inspect yearly balances. Exact figures are also in the table below.
| Year | Starting balance | Contributions | Interest / growth | Ending balance |
|---|---|---|---|---|
| 1 | $10,000.00 | $6,000.00 | $919.19 | $16,919.19 |
| 2 | $16,919.19 | $6,000.00 | $1,419.38 | $24,338.58 |
| 3 | $24,338.58 | $6,000.00 | $1,955.73 | $32,294.31 |
| 4 | $32,294.31 | $6,000.00 | $2,530.85 | $40,825.16 |
| 5 | $40,825.16 | $6,000.00 | $3,147.55 | $49,972.70 |
| 6 | $49,972.70 | $6,000.00 | $3,808.82 | $59,781.53 |
| 7 | $59,781.53 | $6,000.00 | $4,517.90 | $70,299.43 |
| 8 | $70,299.43 | $6,000.00 | $5,278.24 | $81,577.68 |
| 9 | $81,577.68 | $6,000.00 | $6,093.55 | $93,671.22 |
| 10 | $93,671.22 | $6,000.00 | $6,967.79 | $106,639.02 |
| 11 | $106,639.02 | $6,000.00 | $7,905.24 | $120,544.25 |
| 12 | $120,544.25 | $6,000.00 | $8,910.45 | $135,454.70 |
| 13 | $135,454.70 | $6,000.00 | $9,988.32 | $151,443.02 |
| 14 | $151,443.02 | $6,000.00 | $11,144.12 | $168,587.14 |
| 15 | $168,587.14 | $6,000.00 | $12,383.47 | $186,970.62 |
| 16 | $186,970.62 | $6,000.00 | $13,712.41 | $206,683.03 |
| 17 | $206,683.03 | $6,000.00 | $15,137.43 | $227,820.45 |
| 18 | $227,820.45 | $6,000.00 | $16,665.45 | $250,485.91 |
| 19 | $250,485.91 | $6,000.00 | $18,303.94 | $274,789.85 |
| 20 | $274,789.85 | $6,000.00 | $20,060.87 | $300,850.72 |
Compound interest means earning interest on your starting money and on interest already earned. Simple interest applies only to your starting amount. With compounding, earlier interest becomes part of the balance that earns the next round.
Monthly contributions add to that balance. With a positive rate, earlier deposits have more time to grow. Reinvested investment returns can compound too, though returns can fluctuate or be negative.
Start with $10,000 and add $500 at the end of each month. At a hypothetical 7% nominal annual interest rate for 20 years, with monthly compounding, the final balance is $300,850.72.
That’s $130,000.00 you put in—your starting investment plus $120,000 in monthly contributions—and $170,850.72 in hypothetical growth. Try this example.
We divide your nominal annual rate by 12, apply it to the balance each month, then add your monthly contribution. At 0%, your balance is simply everything you put in. A negative rate reduces the balance before each deposit.
Interest / growth is the final balance minus your total invested. The growth percentage compares that difference with your total invested over the full period, not per year.
FV is the final balance; P, the initial investment; M, the monthly contribution; r, the monthly decimal rate (annual percentage ÷ 1,200); and n, the number of months (years × 12).
When r = 0, use FV = P + M × n. Both formulas assume end-of-month contributions. See our methodology for input limits and rounding details.
Interest is added 12 times a year and stays in the balance. A 6% nominal annual rate becomes 0.5% per month; compounding makes the effective annual rate slightly higher than 6%.
At month-end, after that month’s growth. Each deposit starts earning growth the following month. Beginning-of-month deposits would earn one extra month of growth, but aren’t modeled here.
Enter a hypothetical nominal annual rate. The default 7% is an example, not a forecast. APY already includes compounding, so it isn’t interchangeable with a nominal rate.
Interest is paid on deposits or loans. Investment growth can also include price changes and reinvested dividends. This calculator models either with a constant rate.
No. Real investment returns vary, and their timing affects growth. These results show what your chosen fixed rate would produce, not what an investment will earn.