Compound Interest Calculator

Written byOleh Soloninupdated 5 October 2026

Currency

Initial amount

Annual rate, %

Years

Compounding periods per year

Regular contribution

The amount of each contribution; 0 for none.

Contribution frequency

Result

Future value

$50,969.84

Total contributions

$34,000.00

Total growth

$16,969.84

Effective annual rate

6.17%

Formula for the initial amount

10,000 × (1 + 6% ÷ 12)^(12 × 10) = 18,193.97

Year by year

Year         Balance        Paid in       Interest
 1 yr         13,084         12,400            684
 2 yr         16,358         14,800          1,558
 3 yr         19,834         17,200          2,634
 4 yr         23,524         19,600          3,924
 5 yr         27,443         22,000          5,443
 6 yr         31,602         24,400          7,202
 7 yr         36,018         26,800          9,218
 8 yr         40,707         29,200         11,507
 9 yr         45,685         31,600         14,085
10 yr         50,970         34,000         16,970

This result is informational only and is not professional advice.

Starting amount$10,000.00

Contributions$24,000.00

Growth$16,969.84

Interest on interest, with regular contributions and a yearly breakdown

Work out compound interest with regular contributions: the future value, what you paid in and what interest added, the effective annual rate, the formula with your numbers and a year-by-year table.

Compound interest means interest is added to the balance and earns interest itself in the next period. In the first years the difference from simple interest is small, but over long periods it does most of the work: 10,000 at 6% becomes 28,000 with simple interest after 30 years and 57,434.91 with annual compounding.

This calculator grows a starting amount and regular contributions at the compounding frequency you choose. It shows the future value, how much of it you paid in and how much interest added, the effective annual rate, the formula with your numbers and a table year by year.

How to use

Enter the starting amount, the annual interest rate and the number of years.
Enter how many times a year interest is compounded: 12 for monthly, 4 for quarterly, 1 for yearly, 365 for daily.
If you will add money regularly, enter the contribution and how often you make it: monthly, quarterly or yearly. Enter 0 for no contributions.
Read the future value, the split between contributions and interest, the effective rate and the yearly table.

Simple vs compound interest

With simple interest you earn the same amount every year, because it is always worked out on the original sum. With compound interest each year's interest is worked out on the balance including earlier interest, so the yearly amount keeps growing. After one year there is no difference; after 30 years compounding has more than doubled the gain.

10,000 at 6% a year, compounded yearly. Worked out with this calculator.
Years	Simple interest	Compound interest	Difference
1	10,600.00	10,600.00	0.00
5	13,000.00	13,382.26	382.26
10	16,000.00	17,908.48	1,908.48
20	22,000.00	32,071.35	10,071.35
30	28,000.00	57,434.91	29,434.91

The compound interest formula

The balance after t years is A = P × (1 + r ÷ n)^(n × t), where P is the starting amount, r the annual rate as a decimal and n the number of compounding periods a year. 10,000 at 6% compounded monthly for 10 years: 10,000 × (1 + 0.06 ÷ 12)^120 = 18,193.97.

Regular contributions add up as an annuity: FV = PMT × ((1 + i)^N − 1) ÷ i, where PMT is each contribution, i the rate per contribution period and N the number of contributions. When interest compounds more often than you contribute, the calculator converts the rate to your contribution period.

What regular contributions add

Example: 10,000 to start, 200 added every month, 6% a year compounded monthly, for 10 years. You pay in 34,000 in total and end with 50,969.84, of which 16,969.84 is interest. Without the monthly contributions the starting amount alone would reach 18,193.97.

How 10,000 grows at different rates

Over long periods the rate matters enormously: at 10% a year 10,000 grows almost twentyfold in 30 years, at 4% only about threefold. Taxes, fees and inflation are not included.

Monthly compounding, no contributions. Worked out with this calculator.
Rate	1 year	5 years	10 years	20 years	30 years
4%	10,407.42	12,209.97	14,908.33	22,225.82	33,134.98
6%	10,616.78	13,488.50	18,193.97	33,102.04	60,225.75
8%	10,830.00	14,898.46	22,196.40	49,268.03	109,357.30
10%	11,047.13	16,453.09	27,070.41	73,280.74	198,373.99

How often interest compounds

The more often interest is added to the balance, the higher the result, but the gains shrink: going from yearly to quarterly compounding makes a visible difference, going from monthly to daily hardly any. The rate and the time matter far more.

10,000 at 6% a year, no contributions. Worked out with this calculator.
Compounding	Effective annual rate	Balance after 10 years
Yearly	6.00%	17,908.48
Quarterly	6.14%	18,140.18
Monthly	6.17%	18,193.97
Daily (365)	6.18%	18,220.29

The rule of 72

Divide 72 by the interest rate to estimate how many years it takes to double your money. The exact figure with yearly compounding is ln 2 ÷ ln(1 + r). Between 6% and 12% the rule is within about a tenth of a year; at 20% it is about two tenths out.

Exact doubling time with yearly compounding, rounded to a tenth.
Rate	Rule of 72	Exact
4%	18 years	17.7 years
6%	12 years	11.9 years
8%	9 years	9.0 years
10%	7.2 years	7.3 years
12%	6 years	6.1 years
15%	4.8 years	5.0 years
20%	3.6 years	3.8 years

Compound interest and inflation

The result is in today's money only in name: prices rise while it grows. The real rate of return is (1 + rate) ÷ (1 + inflation) − 1, so 6% a year with 3% inflation is a real return of 2.91%, not 3%.

To see what an amount will be worth in future prices, use the inflation calculator; to work out how much to save for a goal, use the savings goal calculator.

What this calculator shows

The future value, your contributions and the interest earned
The effective annual rate for the compounding you chose
The formula for the starting amount with your numbers
A year-by-year table of balance, contributions and interest

What to keep in mind

The rate stays the same for the whole period; taxes, fees and inflation are not included.
Each contribution is made at the end of its period and grows at the rate converted to that period.
The number of compounding periods a year is a whole number, such as 1, 4, 12 or 365.

Where the numbers come from

Checked against the compound interest formula.

FAQs

How do I calculate compound interest?

Use A = P × (1 + r ÷ n)^(n × t). For 10,000 at 6% compounded monthly for 10 years: 10,000 × 1.005^120 = 18,193.97. The calculator shows this formula with your own numbers.

How do I include monthly contributions?

Add the growth of the contributions, PMT × ((1 + i)^N − 1) ÷ i, to the growth of the starting amount. 10,000 plus 200 a month at 6% for 10 years comes to 50,969.84.

How much will 10,000 grow to in 20 years?

At 6% compounded monthly, 33,102.04; at 8%, 49,268.03; at 4%, 22,225.82 — before tax and inflation. Enter your own rate to see yours.

How much do I need to save each month to reach 100,000?

At 6% compounded monthly over 10 years, about 610.21 a month: payment = goal × i ÷ ((1 + i)^N − 1), with i = 0.5% and N = 120. The savings goal calculator works this out for any target.

How much difference does compounding frequency make?

Less than the rate and the time. 10,000 at 6% for 10 years reaches 17,908.48 with yearly compounding and 18,193.97 with monthly; daily compounding adds only another 26.32.

What is the rule of 72?

Divide 72 by the annual rate to estimate the years it takes to double. At 8% that is about 9 years, at 6% about 12. The exact figure at 6% with yearly compounding is 11.9 years.

What is the effective annual rate?

The yearly return including compounding: (1 + r ÷ n)^n − 1. At 6% compounded monthly it is 6.17%. It is the fair way to compare rates with different compounding.

Why does the growth curve steepen later?

Because interest is earned on earlier interest. The first decade looks modest and the later ones do most of the work, which is why starting early matters more than the size of each contribution.

Should I allow for inflation?

Over any long period, yes. The real return is (1 + rate) ÷ (1 + inflation) − 1: 6% with 3% inflation is 2.91% a year in real terms.

Worked example

10,000 plus 200 a month

Input: 10,000 at 6% a year for 10 years, compounded 12 times a year, 200 added monthly

Output: 50,969.84 in total: 34,000 paid in and 16,969.84 of interest

Note: Without the contributions, the 10,000 alone would grow to 18,193.97.

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