Compound Interest Calculator
Enter your starting amount, what you will add each month, the interest rate and the number of years to see your final balance and how much of it is interest.
Enter a deposit or a monthly contribution, the interest rate and the number of years.
Gross result, before taxes. Add an inflation rate to also see what it is worth in today’s money.
Year-by-year breakdown
Enter a deposit or a monthly contribution, the interest rate and the number of years.
Results are estimates. Solvemis accepts no responsibility for the results obtained or for how they are used. Always double-check the result and talk to a qualified professional before making decisions.
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How it works
How to use it
- Enter your starting deposit and how much you will add each month. Either one can be left blank.
- Enter the annual interest rate and the number of years.
- Choose how often interest is compounded and whether you contribute at the start or the end of each month.
- To see what it will be worth in today's money, enter the average inflation you expect. The Federal Reserve targets 2%.
- You will see the final balance, how much you put in and how much is interest, with a chart of how it grows. Open the table for a year-by-year breakdown.
How it is calculated
The balance is simulated month by month. The annual rate is converted to its equivalent monthly rate for the chosen compounding frequency, (1 + r/n)^(n/12) − 1, applied to the balance each month, and then the contribution is added. With no contributions, the result matches the classic compound interest formula exactly. If you enter an inflation rate, each balance is divided by (1 + inflation)^years to express it in today's money.
Final balance = P × (1 + r/n)^(n × years)
Sources
- Compound Interest Calculator — U.S. Securities and Exchange Commission (Investor.gov)
- Why does the Federal Reserve aim for inflation of 2 percent over the longer run? — Board of Governors of the Federal Reserve System
About this calculator
How compound interest works
With compound interest, the interest you earn is added to your balance and starts earning interest itself. In year one you earn interest on what you put in; in year two, on what you put in plus year one’s interest; and so on. The effect is small at first and large over time.
Using this calculator’s own numbers: $10,000 at 5% for 10 years, compounded monthly, grows to $16,470. Add $100 a month and you finish with $31,998 — you contributed $22,000, and nearly $10,000 is interest.
Time matters more than anything else
The formula raises growth to a power that depends on the number of years, which is why starting early beats contributing more later. A handy shortcut is the rule of 72: divide 72 by the interest rate to estimate how many years it takes for money to double. At 5%, about 14 years; at 8%, about 9.
APR, APY and compounding frequency
The nominal rate is the headline annual percentage. The APY (annual percentage yield) is what the account actually earns in a year once compounding is taken into account:
| Compounding | 5% nominal equals |
|---|---|
| Annually | 5.00% APY |
| Quarterly | 5.09% APY |
| Monthly | 5.12% APY |
| Daily | 5.13% APY |
When comparing savings accounts or CDs, compare APY with APY — it is the only figure that puts every product on the same footing. In the calculator you enter the nominal rate and pick the frequency; the result already includes the effect.
Contributing at the start or the end of the month
Money added at the start of a month earns interest for that whole month; money added at the end starts earning the following month. The gap is small but it accumulates: at $100 a month for 10 years at 5%, contributing at the start adds about $65.
Inflation: what your money will actually buy
A dollar in 20 years will not buy what it buys today. Enter the average inflation you expect and the calculator adds a dashed line to the chart and a row to the result showing the value in today’s money: each balance divided by (1 + inflation) raised to the number of years.
The gap between the two lines is what inflation takes. And if your rate does not beat inflation, your balance grows in dollars but loses purchasing power: at 2% interest with 2% inflation, in 10 years you will have more dollars and be able to buy practically the same.
For reference, the Federal Reserve targets 2% inflation over the longer run. Actual inflation can be very different in any given period: in 2022 it peaked above 9% in the United States.
What the result leaves out
- Taxes: interest in a regular account is generally taxable income.
- Inflation, unless you enter it: without it, the result is in future dollars, not today’s purchasing power.
- Fees: fund expense ratios and account fees come straight out of returns.
- Variable returns: the calculator assumes a fixed rate. Investments such as stock funds return different amounts every year, sometimes negative, so treat the result as an illustration rather than a forecast.
Frequently asked questions
What is the difference between simple and compound interest?
Simple interest is always calculated on the original deposit. Compound interest is added to the balance and then earns interest itself. Over 10 years at 5%, $10,000 grows to $15,000 with simple interest and to $16,289 with annual compounding.
Is monthly compounding better than annual?
At the same nominal rate, yes: the more often interest is compounded, the sooner it starts earning interest of its own. That is why banks also quote the APY, which converts any compounding frequency to its annual equivalent. A 5% rate compounded monthly is a 5.12% APY.
Does the result include taxes?
No, it is a pre-tax figure. Interest in a regular account is generally taxed as ordinary income, while tax-advantaged accounts such as IRAs and 401(k)s follow their own rules. Your actual after-tax balance depends on the account and your tax situation.
What about inflation?
It is only taken into account if you enter it. Then you also see what the final balance is worth in today's money: $16,470 in 10 years, with 2% average inflation, buys what $13,511 buys today. For reference, the Federal Reserve targets 2% inflation over the longer run.
Updated September 29, 2026
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