Enter your investment, rate, and time period. See exactly how compound interest grows your wealth.
| Year | Balance | Contributed | Interest Earned |
|---|
Enter what you are starting with, what you add each month, the annual rate and the number of years. Choose how often the interest compounds; monthly is the closest match to a savings account or a monthly-invested brokerage account. The table underneath shows the balance at the end of each year, split into money you put in and money the growth added.
The monthly contribution field is where most of the answer lives. Starting balance is a one-time decision; the monthly amount is a habit, and it compounds every month for as long as you keep it up.
$5,000 to start, $200 a month, 7% a year, compounded monthly, for ten years:
| Measure | Value |
|---|---|
| Starting balance | $5,000 |
| Contributions over 10 years | $24,000 |
| Total put in | $29,000 |
| Final balance | $44,665 |
| Growth | $15,665 |
More than a third of the final balance is growth you never deposited. Push the horizon to twenty years with the same inputs and the growth line overtakes the contributions, which is the entire argument for starting early rather than starting big.
Compounding is interest earning interest. In year one the gain on $5,000 at 7% is small; by year ten the balance is earning on a much larger base, so the same rate produces a much larger number. The rule of 72 is the shorthand: divide 72 by the annual rate and you get the years it takes to double. At 7% that is about 10.3 years, which is why the ten-year example roughly doubles your total input rather than matching it.
The rate is the assumption to be careful with. A 7% return is a planning convention for a diversified long-term portfolio, not a promise, and it is a nominal figure: at 3% inflation the real return is nearer 4%, which pushes the doubling time out to about eighteen years. Any calculator that shows a smooth curve is showing you the average, not the ride. Real portfolios fall in some years, and the order of those falls matters if you are withdrawing.
Fees hide inside the rate. A fund charging 1% a year against one charging 0.05% turns a 7% gross return into 6% net, and over thirty years that difference is a large fraction of the final balance. Enter the return you actually expect after fees.
Less than people think. Monthly against annually at 7% changes the ten-year result by a small amount; the rate and the time do far more work.
For goals, yes. Subtract roughly 2.5–3% from the return to see the result in today's money, or enter a lower nominal rate.
Multiply the annual amount by twelve and put it in as a yearly contribution, or divide by twelve for the monthly field. The timing of contributions changes the total slightly.
It is a common long-run assumption for a diversified stock-heavy portfolio after fees, and it is not a guarantee. Shorter horizons are less predictable, not more.
No. That is a payment calculation with a fixed term, and the loan calculator handles it.
Compound growth is arithmetic. The glossary definition, and the warning that past returns are not a forecast, is the SEC’s investor education site.
Last updated: November 2, 2026. Reviewed by David Liu.