Compound Interest

Project how an initial deposit and regular contributions grow over time, with the compounding frequency of your choice.

$
$/mo
6.0%
25 yr
Future value after 25 years
$391,147
Up 144% on money contributed.
Total contributed
$160,000
Total interest
$231,147
Years
25 yr
Contributions are added at the end of each month and assume a constant annual rate. An estimate, not financial advice.
Balance vs. contributions over time
$500k$250k$0Start13yr25yr
BalanceContributed

The gap between the two lines is interest earned: $231,147 on top of $160,000 paid in.

How the model works

Starting from your initial deposit, the calculator adds your monthly contribution at the end of each month and applies growth for that month before moving to the next. Your chosen compounding frequency (annually, monthly, daily, and so on) is converted to an equivalent monthly rate first, so a contribution added mid-year keeps compounding consistently no matter how often the nominal rate technically compounds. Run that forward for the number of years you set, and you get the future value.

Reading the results

The future value is your ending balance. Total contributed is every dollar you put in yourself: the initial deposit plus every monthly contribution added along the way. Total interest is simply the difference, the money the market added on top of what you put in. The chart plots both the balance and your cumulative contributions over time, so the widening gap between the two lines is a visual read on how much of your final balance is actually interest.

A few caveats

Real returns don't arrive as a smooth constant rate. Some years markets fall, some years they surge, and the order those swings happen in matters more than the average. This calculator also leaves out taxes, fees, and inflation, all of which chip away at the purchasing power of that future balance. A higher compounding frequency at the same nominal rate produces a slightly higher effective rate, which is why daily compounding edges out annual compounding even when the stated interest rate is identical. Use these numbers to compare scenarios against each other, not as a promise of what your account will actually be worth.