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Compound Interest With Monthly Contributions

Most people build savings by adding a set amount each month, not by investing one big sum. This calculator shows what a starting balance and a steady monthly deposit become when the interest keeps earning interest.

The pre-filled figures show a modest start and a regular deposit over a long stretch. Replace them with your own and watch the final balance and the table change.

$
$
%
years
%
Final balance
$271,649
Total you put in
$95,000
Interest earned
$176,649
Year by year
YearTotal put inBalance
1$8,600$9,079
2$12,200$13,453
3$15,800$18,144
4$19,400$23,173
5$23,000$28,566
6$26,600$34,349
7$30,200$40,550
8$33,800$47,199
9$37,400$54,329
10$41,000$61,974
11$44,600$70,172
12$48,200$78,962
13$51,800$88,388
14$55,400$98,495
15$59,000$109,333
16$62,600$120,955
17$66,200$133,417
18$69,800$146,779
19$73,400$161,107
20$77,000$176,472
21$80,600$192,947
22$84,200$210,613
23$87,800$229,555
24$91,400$249,868
25$95,000$271,649
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How the growth is worked out

There are two pieces to the final balance. One is the starting balance of $5,000 growing alone. The other is the stream of $300 deposits growing together. Both use the same monthly rate of 0.5833 percent over 300 months.

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Worked example

Start with $5,000 and add $300 each month for 25 years at 7 percent. You would put in $95,000 yourself. The final balance is $271,649, so $176,649 of it is interest.

Interest makes up 65 percent of that final balance. Most of it arrives in the later years, because the balance is larger by then and has more to earn on.

Questions about this calculator

Does it matter if I deposit at the start or the end of the month?

This calculator adds each deposit at the end of the month. Depositing at the start of the month instead would lift the example balance to $273,066, because each deposit earns one more month of interest.

What happens if I double the monthly deposit?

Raising the deposit from $300 to $600 lifts the example balance from $271,649 to $514,670. The balance does not quite double because the starting amount stays the same.

What if I stop depositing after 10 years?

After 10 years the example balance is $61,974. Left alone for the other 15 years with no deposits, it would grow to about $176,560, compared with $271,649 if you kept going.

What if I start 5 years later?

To reach the same $271,649 in 20 years instead of 25 you would need $482.71 a month instead of $300. Starting earlier does much of the work.

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This page is for education only and is not financial or tax advice.