Compound Interest
See how a balance grows with compound interest and regular deposits. Change any input and the chart, totals and year-by-year table update, and the link updates too so you can share the result.
Hover or focus the chart and use the arrow keys to read each year.
Year-by-year table
| Year | Deposits | Interest | Total deposits | Total interest | Balance | Today’s $ |
|---|
How it works
Each year the calculator adds your deposits and credits interest period by period. Compounding sets how often interest is added to the balance: monthly compounding at 7% works out to an effective 7.23% a year, daily to 7.25%, continuous to 7.25%.
When deposits happen on a different schedule from compounding (say, weekly deposits with monthly compounding), interest is credited at the equivalent rate for each deposit period, (1 + r/n)^(n/f) − 1. Real accounts that pay simple interest between compounding dates can differ by a few dollars.
Start vs end of period matters: a deposit made at the start of each month earns one extra month of interest, so over decades it adds up. Increase each year raises the deposit amount once a year, for example 3% to keep up with pay rises.
Reading the result
Total deposits is your initial deposit plus every contribution. Total interest is everything else. Today’s dollars divides the final balance by cumulative inflation, which shows what it would buy at today’s prices.
The address bar updates as you type, so Copy link shares exactly this scenario. Nothing is sent to a server; the calculation runs in your browser.
Questions
What is the compound interest formula?
For a single deposit, A = P(1 + r/n)nt, where P is the starting amount, r the annual rate as a decimal, n the number of compounding periods per year and t the number of years. Regular deposits add the future value of an annuity on top: PMT × ((1 + i)N − 1) / i, where i is the rate per deposit period and N the number of deposits.
How much will $500 a month grow to in 20 years?
At 7% compounded monthly, $500 deposited at the end of each month for 20 years grows to about $260,000, of which $120,000 is your deposits and the rest is interest. The default inputs on this page show this case with a $10,000 starting balance.
Does compounding frequency make a big difference?
Less than people expect. Moving from annual to monthly compounding at 7% raises the effective rate from 7.00% to 7.23%. Going from monthly to daily adds only about 0.02 points. The rate and the time you stay invested matter far more.
What is the rule of 72?
Divide 72 by the annual rate to estimate how many years money takes to double. At 8%, that is about 9 years. The calculator shows the exact doubling time for your rate under the summary.
Are investment returns really compound interest?
Only roughly. A savings account pays a known rate; stocks and funds return different amounts each year, sometimes negative. Using an average return here gives a smooth path that real markets won’t follow, so treat long-range results as a rough guide.