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Compound Interest Calculator
Compound interest earns interest on your interest. Enter your principal, contributions, rate, and how often it compounds to watch your balance snowball — with the exact split of contributions versus interest.
Short answer
Compound interest is interest calculated on both your original principal and the interest already earned. $10,000 at 5% compounded monthly grows to about $16,470 in 10 years — versus $16,289 compounded yearly. More frequent compounding earns slightly more.
Future balance
$47,527
- Total contributions
- $34,000
- Interest earned
- $13,527
28% of your final balance is interest.
| Year | Contributions | Interest | Balance |
|---|---|---|---|
| 1 | $12,400 | $567 | $12,967 |
| 2 | $14,800 | $1,287 | $16,087 |
| 3 | $17,200 | $2,165 | $19,365 |
| 4 | $19,600 | $3,212 | $22,812 |
| 5 | $22,000 | $4,435 | $26,435 |
| 6 | $24,400 | $5,843 | $30,243 |
| 7 | $26,800 | $7,446 | $34,246 |
| 8 | $29,200 | $9,254 | $38,454 |
| 9 | $31,600 | $11,277 | $42,877 |
| 10 | $34,000 | $13,527 | $47,527 |
About the compound interest calculator
The formula is A = P(1 + r/n)^(nt): principal P, annual rate r, n compounding periods per year, and t years — plus the future value of any regular contributions. This calculator runs it for you and shows the year-by-year balance, so you can see how small, consistent deposits and time do most of the work. Try changing the compounding frequency from yearly to daily to see how much it moves the result.
Growth of $10,000 + $200/mo at 5% (compounded monthly)
| After | You contribute | Interest earned | Balance |
|---|---|---|---|
| 10 years | $34,000 | $13,527 | $47,527 |
| 20 years | $58,000 | $51,333 | $109,333 |
| 30 years | $82,000 | $129,129 | $211,129 |
Pre-tax growth using monthly compounding. Interest earned is the balance minus everything you put in — it overtakes contributions the longer you save.
How we calculate this
This calculator grows your balance the way a savings account does:
- Compounding. each period the balance earns interest at rate ÷ periods-per-year, and that interest is added back so it compounds. A = P(1 + r/n)^(nt).
- Contributions. your monthly deposit is added every period and grows from the moment it lands — the future value of a series of deposits, added to the growth of your starting balance.
- Interest vs contributions. total interest = final balance − everything you deposited (starting balance plus all contributions), so you can see how much your money earned on its own.
Assumptions
- A constant rate for the whole term — real savings rates change.
- Pre-tax — interest in a taxable account is taxed as income the year you earn it.
- Contributions are made monthly and stay the same.
Sources
Last reviewed: July 17, 2026
Frequently asked questions
How is compound interest calculated?+
Compound interest uses A = P(1 + r/n)^(nt): your principal P grows by the annual rate r, compounded n times a year, over t years. Because each period's interest is added to the balance, the next period earns interest on that interest too. This calculator also adds the growth of any regular monthly deposits, then shows the total interest earned separately from what you put in.
What's the difference between APY and interest rate?+
The interest rate is the base annual rate; APY (annual percentage yield) folds in the effect of compounding, so it's the rate you actually earn over a year. A 5% rate compounded monthly is about a 5.12% APY. If your bank quotes an APY, enter it with yearly compounding to match; if it quotes a rate, choose how often it compounds.
How much will my savings grow?+
It depends on four things: your starting balance, how much you add each month, the interest rate, and how long you leave it. Time and regular contributions usually matter more than the rate — $200 a month at 5% for 30 years grows to roughly $166,000, and about half of that is interest. Enter your own numbers above to see your result and a year-by-year table.
Does compounding frequency really matter?+
A little. $10,000 at 5% for 10 years grows to about $16,289 compounded yearly, $16,470 compounded monthly, and $16,487 compounded daily. Daily beats yearly, but the gap is small compared to the rate itself and how long you save. This tool lets you switch the frequency to see the exact difference.
Is the interest I earn taxable?+
In a regular (taxable) savings account, interest is generally taxed as ordinary income in the year you earn it, which lowers your effective return. Tax-advantaged accounts (like a Roth IRA or 401(k)) change that. This calculator shows pre-tax growth — check your own tax situation for the after-tax figure.
How do regular monthly deposits change the result?+
Every deposit you add starts compounding from the moment it lands, so consistent contributions have an outsized effect over time. The calculator treats your monthly deposit as recurring and shows total contributions and total interest separately, so you can see exactly how much of your final balance you saved versus earned.
Also try the Savings Calculator, or plan paying down what you owe with the debt payoff calculator.