Compound Interest Calculator
Calculate growth with compound interest
Compound Interest Calculator tool
Results
Final Amount
$0.00
Total Interest
$0.00
Total Deposits
$0.00
Compound Interest Calculator: key facts
- What it does
- Calculate growth with compound interest
- Category
- Financial Calculators
- Cost
- Free, with no account, sign-up, or install.
- Your data
- Runs entirely in your browser — the files and text you enter are never uploaded to a server.
- Last reviewed
- . Report an incorrect result.
Understanding the Compound Interest Calculator
Compound interest is the reason a modest sum left alone can grow into something substantial — interest earns interest, and the effect snowballs over time. This calculator projects that growth from a principal amount, a rate, and a time horizon, and optionally layers in a monthly deposit so you can model a balance that you keep feeding.
Savers use it to see what a deposit becomes in a decade; investors use it to compare how compounding frequency nudges the outcome. The year-by-year growth table is where it earns its keep, turning an abstract formula into a visible curve so you can watch the gap between contributions and earned interest widen each year.
Getting a result
- Enter your principal — the starting amount.
- Enter the annual interest rate and the number of years.
- Pick a compounding frequency: daily, monthly, quarterly, or annually.
- Optionally add a monthly deposit to model ongoing contributions.
- Read the final amount, total interest, and total deposits, and expand the year-by-year table to see the growth build.
How compounding is applied here
With no periodic deposit, this is the textbook compound interest calculation. The annual rate is divided by the number of compounding periods you select, and the exponent is that same count multiplied by the number of years, so daily, monthly, quarterly and annual settings each produce a slightly different result from identical inputs.
Adding a monthly deposit changes the calculation in a way worth knowing about: the tool switches to monthly compounding regardless of the frequency selected in the dropdown, then treats the balance as two parts. The opening amount grows on its own, and the stream of deposits is valued as an ordinary annuity — each deposit compounding for however many months remain after it arrives.
The yearly growth table applies the same arithmetic at each year boundary rather than interpolating, so the deposits column and the interest column in any row always reconcile against the balance.
- $10,000 at 5% for 10 years compounded annually — the page defaults — reaches $16,288.95, so $6,288.95 is interest.
- Switch that same entry to daily compounding and it reaches about $16,486: roughly $197 more, which is all the frequency setting is worth at this rate.
- Add $100 a month to the default and the balance becomes $31,998.32. Of that, $22,000 is money you put in and $9,998.32 is growth.
Reasons to use it here
- It breaks results into final amount, total deposits, and total interest, so you can see precisely how much growth came from compounding versus from your own money.
- The year-by-year table makes the exponential curve concrete rather than leaving it as a single end figure.
- It supports four compounding frequencies for a lump sum, illustrating how more frequent compounding edges the total higher.
- Calculations are local and instant, so your figures stay on your device.
Reading the projection honestly
The single largest weakness of any compounding projection is that it assumes one unchanging rate for the whole term. Real returns arrive unevenly, and the order in which good and bad years fall changes the outcome even when the average is identical. A ten-year figure from this page is one scenario, not a forecast.
Nothing here accounts for inflation, so a balance a decade out is quoted in tomorrow's money rather than today's purchasing power. Tax on interest or gains is also excluded, as are platform and fund charges — and a one-percent annual fee removes considerably more over a long term than most people expect.
Frequently Asked Questions
What is compound interest?
Compound interest is interest calculated on both your original principal and the interest already added to it. Unlike simple interest, which is charged only on the principal, compounding means your balance grows on itself, accelerating over time.
How does compounding frequency affect growth?
More frequent compounding credits interest sooner, so it begins earning its own interest earlier. At the same annual rate, daily compounding produces slightly more than annual compounding — the difference is modest over short periods but adds up over many years.
Does adding a monthly deposit change the calculation?
Yes. When you add a monthly deposit, the tool models your contributions as a monthly series growing alongside the principal, which reflects a regular saving habit rather than a single untouched sum. Total deposits are reported separately so you can see your contribution clearly.
What is the rule of 72?
It is a quick mental shortcut: divide 72 by your annual interest rate to estimate the years it takes for money to double. At 6%, that is roughly 12 years. This calculator gives the exact figure, but the rule is a handy sanity check.
