Compound Interest Calculator
Compound interest calculator: see how savings grow with monthly contributions and inflation-adjusted value. Free, no sign-up, and it runs in your browser.
Dedicated page: /en/compound-interest-calculator
Default checked 10 Nov 2026: 7% (long-run US stock market average after inflation, about 10% before inflation). Leave it, or enter your exact rate if you know it. Check the current value here.
Default checked 10 Nov 2026: 3% assumed. Latest US inflation is 3.7% (12 months to September 2026). Leave 3%, or enter the current rate. Clear the box to hide today's dollars. Check the current value here.
Reverse: how much monthly to reach a goal?
Quick answer
A compound interest calculator shows what savings grow to when interest earns interest. Enter a starting deposit, a monthly contribution, an annual rate and a number of years, and it gives the future value, the interest earned, a year-by-year table and the value in today's dollars.
About this Compound Interest Calculator
Compound interest calculator: see how savings grow with monthly contributions and inflation-adjusted value. It is one of the Money and Finance on ToolUstad, and like every tool here it runs entirely in your browser: nothing you type, paste or open is uploaded to a server, and there is no sign-up or usage limit.
What is a compound interest calculator?
Compound interest is the growth of money when the interest it earns is added to the balance, so the next period earns interest on a bigger amount. It is the difference between saving under a mattress and saving in an account: the mattress balance grows only by what you add, while the account balance grows by what you add plus interest on everything already there.
This calculator handles the real-world version, not the textbook version. It takes an initial deposit and a monthly contribution, because that is how people actually save, and it compounds daily, monthly, quarterly or annually, because accounts differ. It shows the year-by-year table so you can see the moment interest overtakes contributions, it converts the final figure into today's dollars so inflation does not fool you, and it runs backwards too, working out the monthly amount needed to reach a target by a date you choose.
How does compound interest maths work?
The future value has two parts. The starting deposit grows by the compound factor, which is one plus the rate per period, raised to the number of periods. The monthly contributions form an annuity: each contribution grows for the periods remaining after it is paid, and the sum of all of them is the contribution times the compound factor minus one, divided by the rate per period. With $10,000 at 7% compounded monthly for 20 years, the deposit alone becomes $40,387. Add $200 a month and the total reaches $144,569, because the contributions themselves earn interest for years after they are paid in.
When and why to use a compound interest calculator
- Starting a retirement account: see what starting ten years earlier is worth, because the first decade's growth compounds the longest.
- Setting a savings goal: use the reverse mode to find the monthly amount that reaches a house deposit or a college fund by a date.
Best practices
- Use a realistic rate: the US stock market has averaged about 7% a year after inflation over the long run, but savings accounts pay far less, and no rate is guaranteed.
- Count contributions you will actually keep up. A plan that needs $500 a month and fails in year two is worse than a $200 plan that survives.
- Always look at the today's-dollars figure before celebrating a big future number, because inflation takes roughly half the value over 20 years at 3% a year.
Common mistakes to avoid
- Using simple interest by mistake: simple interest pays only on the original deposit, and it understates long-term growth by tens of thousands of dollars.
- Assuming the rate stays constant: markets rise and fall, so treat any long forecast as a range, not a promise.
Who is the compound interest calculator for?
Anyone saving for retirement, a house deposit, a child's education, or any goal more than a few years away. The tool is an estimator, not financial advice: it cannot predict markets, and it does not account for tax, fees or inflation beyond the inflation rate you enter.
Current values, checked 10 Nov 2026: the 7% default is the long-run US stock market average after inflation (about 10% before inflation), the savings preset is 4.4% (the top high-yield savings APY), and the inflation box defaults to 3% while the latest US figure is 3.7%. Every rate box is an optional override: leave the default, or enter your exact rate and the calculation uses it.
Learn: how to use the Compound Interest Calculator
- Enter your starting deposit and how much you will add each month, then the annual interest rate and the number of years.
- Pick how often interest compounds: monthly is the usual choice for savings accounts, daily for high-yield accounts.
- Read the future value, then scroll the year-by-year table to see interest take over from contributions in the later years.
Features
- Initial deposit plus monthly contributions, with daily, monthly, quarterly or annual compounding
- Year-by-year table and growth chart, downloadable as CSV
- Inflation-adjusted value in today's dollars at 3% inflation
- Reverse mode: monthly contribution needed to reach a target amount
- Side-by-side total with and without monthly contributions
Worked example
Start with $10,000, add $200 a month, earn 7% compounded monthly for 20 years: the balance reaches $144,573. You put in $58,000 and interest adds $86,573. Without the monthly contributions the same $10,000 would only reach $40,387.
Frequently asked questions
What is compound interest?
Compound interest is interest earned on interest. Each period the interest is added to the balance, so the next period earns interest on a bigger balance. Over decades that snowball is what turns steady monthly saving into real wealth.
Why does the chart curve upward?
Because the balance grows, each year earns more interest than the year before, even though the rate never changes. In the example above the first year earns about $900 of interest and the twentieth year earns about $9,700.
What rate should I use?
Use the rate your account actually pays, or a long-run average for the investment: the US stock market has averaged about 10% a year before inflation, or about 7% after inflation, over the long run, and the top high-yield savings accounts pay about 4.4% now. The preset buttons above set 4.4% for savings or 10% for stocks. Never use a rate a seller promised you.
What does today's dollars mean?
Prices rise about 3% a year on average. $144,573 in 20 years buys what about $80,046 buys today. The inflation box shows that figure so you compare the goal against prices you know now. The latest US inflation rate is 3.7% (12 months to September 2026).
What is the rule of 72?
Divide 72 by the annual rate to estimate how many years it takes money to double. At 7%, money doubles in about 10 years. At 3.5%, it takes about 20 years. It is a quick check, not a replacement for the calculator.
Is daily compounding much better than monthly?
Barely. At 7% over 20 years, daily compounding adds only a few hundred dollars to a $144,000 balance compared with monthly. The rate and the contributions matter far more than the compounding frequency.
Should I pay off debt or invest?
Compare the rates: if a credit card charges 22% and an investment returns 7%, paying the card wins by a wide margin. If a mortgage charges 6% and the investment returns 7%, the answer is closer, and the right choice depends on risk and tax.
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