How to use this calculator
Enter what you start with, what you add each month, the yearly rate you expect and how often interest compounds. The result shows your ending balance, how much of it you deposited, and how much came from interest, with a year-by-year table.
Time does most of the work
| $10,000 start + $200 a month at 7%, compounded monthly | Final balance | You deposited | Interest earned |
|---|---|---|---|
| 10 years | $54,713.58 | $34,000 | $20,713.58 |
| 20 years | $144,572.72 | $58,000 | $86,572.72 |
| 30 years | $325,159.17 | $82,000 | $243,159.17 |
Between years 20 and 30 in this example, the balance grows by more than $180,000 while you add only $24,000. That is compounding: interest starts earning interest of its own.
Does compounding frequency matter?
| $10,000 at 7% for 10 years, no deposits | Final balance |
|---|---|
| Daily | $20,136.18 |
| Monthly | $20,096.61 |
| Quarterly | $20,015.97 |
| Annually | $19,671.51 |
More frequent compounding helps, but much less than the rate, the time and how much you add. When comparing savings accounts, compare the APY, which already includes compounding.
How much will I have if I save each month?
| Saved each month (starting from $0, 7% a year) | After 10 years | After 20 years | After 30 years |
|---|---|---|---|
| $100 | $17,308 | $52,093 | $121,997 |
| $200 | $34,617 | $104,185 | $243,994 |
| $500 | $86,542 | $260,463 | $609,985 |
| $1,000 | $173,085 | $520,927 | $1,219,971 |
At $200 a month you deposit $72,000 over 30 years; the other $171,994 is compound interest. Change the rate in the calculator to match your own account or a more cautious estimate.
The rule of 72
A quick way to estimate how long money takes to double: divide 72 by the yearly rate. At 7%, that is about 10.3 years (the exact figure with yearly compounding is 10.2). At 4%, about 18 years. It is a mental shortcut, not a guarantee, and it works best for rates between roughly 4% and 12%.
Investment returns are not guaranteed, and a savings account rate can change. Taxes, fees and inflation reduce what you keep. For a fixed target, try our savings goal calculator.