Compound Interest Calculator

See how your money could grow with compound interest from a starting balance, regular contributions, an annual rate and a time horizon. You'll get the ending balance, how much you put in and how much came from interest, with a year-by-year table and chart.

FreeNo sign-upInstant resultsUpdated: October 15, 2026

Calculator

Initial deposit

Regular contribution

Frequency

Annual interest rate

Nominal annual rate, before compounding.

Years

years

Compounding

Final balance

$20,514.24

Total contributions

$13,000.00

Interest earned

$7,514.24

Growth over contributions: 57.8%
Effective annual rate (EAR/APY): 8.3%
Money multiplier: 1.58x

Contributions Accumulated interestMax: $20,514

Balance by year
Year	Contributed	Interest	Balance
1	$2,200	$128	$2,328
2	$3,400	$366	$3,766
3	$4,600	$724	$5,324
4	$5,800	$1,211	$7,011
5	$7,000	$1,838	$8,838
6	$8,200	$2,616	$10,816
7	$9,400	$3,559	$12,959
8	$10,600	$4,679	$15,279
9	$11,800	$5,992	$17,792
10	$13,000	$7,514	$20,514

This is a math simulation with a constant rate. Actual returns vary and can be negative; it's not a promise of returns.

Keep analyzing

This is a math simulation at a constant rate, for information only. It is not a promise of returns or investment advice. Real returns vary, can be negative and are often reduced by taxes and fees.

What is compound interest?

Compound interest is interest earned on both your original deposit and the interest already added to it. Each period, interest is added to the balance, and the next period it earns interest too. That is why growth speeds up over time.

With simple interest, $1,000 at 10% a year earns $100 every year. With annual compounding, it earns $110 in year two and $121 in year three, and after 10 years the balance is $2,593.74 instead of $2,000.

What each input means

Initial deposit: the amount you start with today.
Regular contribution: what you add every month or every year. It can be zero.
Annual interest rate: the nominal annual rate (for example, 8%).
Years: how long the money stays invested.
Compounding frequency: how often interest is added to the balance (annually, monthly, daily and so on). More frequent compounding gives a slightly higher result.

Contributions are made at the end of each period, and the simulation moves step by step using the equivalent rate for that period. The table shows the balance at the end of each year, and the chart separates what you contributed from what interest earned.

Compound interest formula

Future value = P × (1 + r/n)^(n×t)
With a contribution C each period: + C × [((1 + i)^k − 1) ÷ i]
where i = rate per period and k = number of contributions

P = initial deposit, r = annual rate (decimal), n = compounding periods per year, t = years.

The effective annual rate shown in the results is (1 + r/n)^n − 1, the actual yearly return once compounding is taken into account. A 10% nominal rate compounded monthly works out to 10.47% a year.

How to read the results

Total contributions: the money that came out of your pocket (initial deposit plus contributions).
Interest earned: what compounding produced. The longer the horizon, the larger its share of the balance.
Growth: interest earned divided by total contributions. 100% means interest doubled what you put in.

$1,000 + $100/month at 8%	Contributed	Interest earned	Ending balance
10 years	$13,000	$7,514	$20,514
20 years	$25,000	$38,829	$63,829
30 years	$37,000	$122,972	$159,972

Rule of 72: divide 72 by the annual rate to estimate how many years it takes to double your money. At 8%, about 9 years.

Example

You start with $1,000 and add $100 a month for 10 years at 8% a year, compounded monthly. You'd end up with about $20,514: you contributed $13,000 and interest added about $7,514, a 57.8% gain on what you put in.

Monthly rate: 8% ÷ 12 ≈ 0.667%
Periods: 10 years × 12 = 120 months
Each month: balance × 1.00667 + $100
Result: about $20,514 (contributed $13,000, interest $7,514)

Common mistakes

Entering a monthly rate as if it were annual, or the other way around. A 2% monthly rate compounds to about 26.8% a year, not 2%.
Ignoring inflation. Your balance may grow much faster than its purchasing power.
Leaving out taxes and fees, which reduce the interest you actually keep and weaken the compounding effect.
Assuming the rate stays constant. Real investments have good and bad years; this is a scenario, not a forecast.
Withdrawing the interest. Once you take it out, it stops compounding.

Frequently asked questions

What is the difference between simple and compound interest?

Simple interest is always calculated on the original amount. Compound interest is calculated on the original amount plus accumulated interest, so it grows faster and faster. Over long periods the gap is huge.

Does compounding frequency matter much?

Somewhat, but less than you might think. $1,000 at 10% for one year becomes $1,100.00 with annual compounding and $1,104.71 with monthly compounding. The rate and the time horizon matter far more.

How much will I have if I save a set amount every month?

Enter what you already have as the initial deposit (or 0), your monthly savings as the contribution, a realistic rate and the number of years. The ending balance is the estimate; total contributions is what you saved yourself.

What interest rate should I use?

Use the rate of the specific product, such as a savings account or CD. For investments without a fixed rate, try several scenarios (for example 4%, 7% and 10%) and compare. Higher expected returns come with more risk and volatility.

Keep going with the next step.