Compound Interest Calculator - Free Online Tool

Year-by-year balance
Year	Contributed	Interest earned	Balance
1	$12,400.00	$801.42	$13,201.42
2	$14,800.00	$1,834.27	$16,634.27
3	$17,200.00	$3,115.28	$20,315.28
4	$19,600.00	$4,662.39	$24,262.39
5	$22,000.00	$6,494.83	$28,494.83
6	$24,400.00	$8,633.24	$33,033.24
7	$26,800.00	$11,099.74	$37,899.74
8	$29,200.00	$13,918.03	$43,118.03
9	$31,600.00	$17,113.55	$48,713.55
10	$34,000.00	$20,713.58	$54,713.58
11	$36,400.00	$24,747.34	$61,147.34
12	$38,800.00	$29,246.20	$68,046.20
13	$41,200.00	$34,243.79	$75,443.79
14	$43,600.00	$39,776.14	$83,376.14
15	$46,000.00	$45,881.93	$91,881.93
16	$48,400.00	$52,602.60	$101,002.60
17	$50,800.00	$59,982.60	$110,782.60
18	$53,200.00	$68,069.60	$121,269.60
19	$55,600.00	$76,914.70	$132,514.70
20	$58,000.00	$86,572.72	$144,572.72

Year-by-year balance

Year

Contributed

Interest earned

Balance

$12,400.00

$801.42

$13,201.42

$14,800.00

$1,834.27

$16,634.27

$17,200.00

$3,115.28

$20,315.28

$19,600.00

$4,662.39

$24,262.39

$22,000.00

$6,494.83

$28,494.83

$24,400.00

$8,633.24

$33,033.24

$26,800.00

$11,099.74

$37,899.74

$29,200.00

$13,918.03

$43,118.03

$31,600.00

$17,113.55

$48,713.55

$34,000.00

$20,713.58

$54,713.58

$36,400.00

$24,747.34

$61,147.34

$38,800.00

$29,246.20

$68,046.20

$41,200.00

$34,243.79

$75,443.79

$43,600.00

$39,776.14

$83,376.14

$46,000.00

$45,881.93

$91,881.93

$48,400.00

$52,602.60

$101,002.60

$50,800.00

$59,982.60

$110,782.60

$53,200.00

$68,069.60

$121,269.60

$55,600.00

$76,914.70

$132,514.70

$58,000.00

$86,572.72

$144,572.72

About the Compound Interest Calculator

Compound interest means you earn interest on the interest you already earned. Over long periods this snowball effect dominates: a balance that doubles every ten years is worth eight times as much after thirty. This calculator shows that curve for your own numbers, including regular monthly contributions, and separates what you put in from what growth added.

The formula for a lump sum is A = P (1 + r/n)^nt, where P is the starting amount, r the annual rate, n the number of compounding periods per year and t the number of years. Contributions are added at the end of each month and then compound alongside the balance. The effective annual rate (APY) shown in the results is what the nominal rate becomes once compounding is taken into account.

Use it to plan retirement savings, a house deposit, a child's education fund or simply to compare accounts with different compounding schedules.

How to use the Compound Interest Calculator

Enter your starting balance and how much you will add every month (zero is fine).
Set the expected annual interest rate, how often it compounds and the number of years.
Read the final balance, the split between contributions and interest, and explore the yearly chart and table.

Frequently asked questions

What is the rule of 72?

A quick mental shortcut: divide 72 by the annual interest rate to estimate how many years it takes money to double. At 6% it doubles in about 12 years; at 9% in about 8 years.

Does compounding frequency matter much?

Less than people expect. At 6%, annual compounding yields exactly 6.00% per year, monthly 6.17% and daily 6.18%. The interest rate and the time horizon matter far more than the frequency.

Are contributions made at the start or end of each month?

At the end of each month, after that month's growth is applied. This is the common "ordinary annuity" assumption used by most banks and planning tools.

What return should I assume for stocks?

Long-run broad stock-market returns have historically averaged roughly 7% per year after inflation, but returns vary widely year to year and past performance does not guarantee future results. Use a conservative figure for planning.