Compound Interest Calculator
Enter what you have, what you'll add, and a rate, and this calculator shows what compounding does to it, with the growth charted and every year's math written out below. Results update as you type; there's nothing to submit.
What you're putting in today
Added every month. Set to 0 for none.
Your expected yearly rate, before compounding
How long the money stays invested
How often interest is added to the balance
Future value
- Starting amount$0
- Total contributions$0
- Interest earned$0
The gap between the two lines is compound interest. Hover or tap the chart for any year's figures.
An estimate from your inputs. Real accounts round to the cent and post interest on their own schedules.
| Year | Paid in | Interest that year | Balance |
|---|
All calculators on this site
- Compound Interest CalculatorThe main tool: growth with contributions at any compounding frequency.
- Daily Compound Interest CalculatorLocked to daily compounding, with a daily-vs-monthly comparison.
- Compound Interest Calculator With WithdrawalsGrowth while taking regular money out, with depletion detection.
- Simple Interest CalculatorThe I = Prt version, with a live comparison against compounding.
- Compound Interest Formula, ExplainedThe math behind every tool here, with worked examples.
How this calculator works
The calculator applies the standard compound interest formula, A = P(1 + r/n)nt, then layers your contributions on top period by period. P is your starting amount, r is the annual rate as a decimal, n is how many times per year interest compounds, and t is the number of years. Contributions are added each month and start compounding from the period they arrive.
Results update as you type. There is no Calculate button because compounding questions are rarely one-shot: the useful part is nudging the rate or the years and watching what changes. The year table below the calculator is the same computation written out the long way, so you can check any year's math yourself.
Every projection here is an estimate built on the rate you enter. Real accounts round differently, post interest on their own schedules, and investment returns vary year to year. The S&P 500 preset uses 10% because that is the index's widely cited long-run average annual return (about 10% since 1957, per Fidelity, with dividends reinvested), not because any future return is promised. After inflation, that long-run figure is closer to 6.5% to 7%. More on who builds and checks these tools is on the about page.
This calculator was built by Cedrick Reese of Ready Utilities. The formula and its worked results are checked against the U.S. Securities and Exchange Commission's compound interest calculator at investor.gov, and the year table is generated by the same code that produces the headline figure, so the two can never disagree. Rate context cited on this page comes from the sources linked beside each claim and is reviewed on a maintenance cycle. Last reviewed: September 1, 2026.
Frequently asked questions
How much will $10,000 grow to in 20 years?
It depends entirely on the rate and compounding schedule. At 5% compounded monthly with no additions, $10,000 becomes about $27,126 in 20 years. At 7% it is about $40,387. Enter your own numbers above and the calculator shows the exact path year by year.
Can I become a millionaire by investing $1,000 a month?
The math says yes, with enough time and a high enough return. At a 7% annual return compounded monthly, $1,000 a month reaches $1 million in about 28 years the way this calculator counts it, with each contribution added at the start of its month. At 10%, about 23 years. These are estimates built on a steady assumed return, which real investments do not deliver in a straight line.
What is the 8-4-3 rule of compound interest?
It is an illustration, popular in investing content, of how compounding accelerates: at roughly a 12% annual return, an investment gains as much in years 9 through 12 as it did in the first 8 years, and as much again in the following 3. It assumes a constant 12% return, so treat it as a teaching pattern, not a promise. Try 12% in the calculator above and read the year table to watch the same acceleration.
Does this work for a savings account?
Yes. Enter your account's rate (banks quote APY, which already includes compounding) and pick the compounding frequency your bank uses. Many savings accounts compound daily and post the interest monthly. For a daily-specific version, use our daily compound interest calculator.