Compound Interest Calculator

See how savings or investments can grow when interest earns interest. Enter a starting amount, regular deposits, a yearly rate and the years, then read the final balance, a yearly chart and a year-by-year table.

Starting amount

Monthly deposit (optional)

Interest rate per year

Years

Years:Compounded

Future value after 20 years

$125,510.22

You put in $58,000.00 and earn $67,510.22 in interest, which is 54% of the final balance.

Final balance: $125,510.22
Total you put in: $58,000.00
Interest earned: $67,510.22
Growth: 2.16×

Point at a bar to read the numbers.

Money you put in Interest earnedHorizontal axis: years

Rule of 72: at 6% a year, money roughly doubles every 12.0 years.

Show year-by-year table

Year	Money put in	Interest	Balance
0	$10,000.00	$0.00	$10,000.00
1	$12,400.00	$683.89	$13,083.89
2	$14,800.00	$1,557.99	$16,357.99
3	$17,200.00	$2,634.03	$19,834.03
4	$19,600.00	$3,924.46	$23,524.46
5	$22,000.00	$5,442.51	$27,442.51
6	$24,400.00	$7,202.21	$31,602.21
7	$26,800.00	$9,218.48	$36,018.48
8	$29,200.00	$11,507.14	$40,707.14
9	$31,600.00	$14,084.97	$45,684.97
10	$34,000.00	$16,969.84	$50,969.84
11	$36,400.00	$20,180.66	$56,580.66
12	$38,800.00	$23,737.54	$62,537.54
13	$41,200.00	$27,661.83	$68,861.83
14	$43,600.00	$31,976.19	$75,576.19
15	$46,000.00	$36,704.68	$82,704.68
16	$48,400.00	$41,872.83	$90,272.83
17	$50,800.00	$47,507.78	$98,307.78
18	$53,200.00	$53,638.30	$106,838.30
19	$55,600.00	$60,294.96	$115,894.96
20	$58,000.00	$67,510.22	$125,510.22

This is an illustration at a steady rate, with deposits at the end of each month. Real returns vary from year to year, and fees and taxes are not included.

How compound interest works

With simple interest you earn interest only on the money you started with. With compound interest, the interest is added to the balance, and from then on the interest earns interest too. The longer the money stays invested, the faster it grows. That is why starting early matters more than almost anything else in saving.

The formula

Future value = P × (1 + r ÷ n)^(n × t), where P is the starting amount, r the yearly rate as a decimal, n the number of times interest is added per year and t the years.
Example: $10,000 at 5% compounded monthly for 10 years = 10,000 × (1 + 0.05 ÷ 12)^120 = about $16,470.
With regular deposits the calculator adds each deposit at the end of the month and keeps growing the balance month by month.

What $10,000 grows to with no deposits

Interest compounded monthly. Small changes in the rate and the years make a big difference.

Years	4%	6%	8%
5	$12,210	$13,489	$14,898
10	$14,908	$18,194	$22,196
20	$22,226	$33,102	$49,268
30	$33,135	$60,226	$109,357

The rule of 72

A quick way to estimate how long money takes to double is to divide 72 by the yearly rate. At 6% it takes about 12 years, and at 8% about 9 years. The calculator shows this under the chart.

Tips for using the results

Try different years: the biggest jump usually comes from adding time, not from a slightly higher rate.
Compare a small monthly deposit with a bigger one to see how much of the final balance is your own money.
Remember inflation: a balance in 30 years buys less than the same amount today.
Fees, taxes and changing returns are not included, so real results will differ.

How to calculate compound interest in Excel or Google Sheets

For a lump sum, use =FV(rate/12, years*12, 0, -principal) with the yearly rate in a cell (for example 5%). To include a monthly deposit, put it in the third argument as a negative number: =FV(rate/12, years*12, -deposit, -principal).

How to use the Compound Interest Calculator tool

Type your starting amount and, if you will add money regularly, a monthly deposit.
Enter the yearly interest rate and the number of years, and choose how often interest is added.
Read the future value, how much you put in and how much is interest.
Point at the chart to see each year, or open the table for the numbers.

Frequently asked questions

What is compound interest?

Compound interest is interest on both your original money and the interest it has already earned. Each period the balance grows a little more, so growth speeds up over time.

What is the compound interest formula?

For a lump sum, the future value is the starting amount × (1 + rate ÷ n)^(n × years), where n is how many times a year interest is added. $10,000 at 5% compounded monthly for 10 years grows to about $16,470.

Does compounding more often make a big difference?

A little. Daily compounding earns slightly more than monthly, and monthly slightly more than yearly. The rate and the number of years matter far more than the compounding frequency.

How are the monthly deposits treated?

Deposits are added at the end of each month and then earn interest from the next month. The balance is worked out month by month using the monthly rate that matches your yearly rate and compounding.

Can I rely on these results for my investments?

No. The calculator assumes the same rate every year. Real investments go up and down, and fees and taxes are not included. Treat the result as an illustration, not a promise.