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What does $100 a month grow to in 30 years at 6%?

$100 a month at 6% a year, compounded monthly, grows to $100,452 in 30 years: $36,000 paid in and $64,452 of interest.

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The numbers for these inputs

YearTotal paid inInterest so farBalance
1$1,200$34$1,234
2$2,400$143$2,543
3$3,600$334$3,934
4$4,800$610$5,410
5$6,000$977$6,977
6$7,200$1,441$8,641
7$8,400$2,007$10,407
8$9,600$2,683$12,283
9$10,800$3,474$14,274
10$12,000$4,388$16,388
11$13,200$5,432$18,632
12$14,400$6,615$21,015
13$15,600$7,945$23,545
14$16,800$9,430$26,230
15$18,000$11,082$29,082
16$19,200$12,909$32,109
17$20,400$14,923$35,323
18$21,600$17,135$38,735
19$22,800$19,558$42,358
20$24,000$22,204$46,204
21$25,200$25,087$50,287
22$26,400$28,223$54,623
23$27,600$31,625$59,225
24$28,800$35,312$64,112
25$30,000$39,299$69,299
26$31,200$43,607$74,807
27$32,400$48,255$80,655
28$33,600$53,263$86,863
29$34,800$58,654$93,454
30$36,000$64,452$100,452

How it works

Each month the balance earns interest at one twelfth of the yearly rate, and that interest is added to the balance, so next month's interest is paid on a slightly larger amount. Any monthly deposit is added at the end of the month.

In short: new balance = old balance x (1 + rate / 12) + deposit, repeated once per month for the number of years you choose. The table shows the balance at the end of each year.

The calculator assumes a fixed rate and no fees, taxes or withdrawals. Real accounts and funds change rate over time, so treat the result as an illustration of the mechanism, not a forecast.

Common mistakes

  • Comparing a nominal yearly rate with an effective one (APY): the same 5% is a little higher once it compounds monthly.
  • Forgetting inflation: a balance that doubles in 14 years buys less than it appears to.
  • Assuming an investment return is guaranteed. Savings accounts pay a stated rate; stocks and funds do not.
  • Ignoring fees: a 1% yearly fee takes a large share of the growth over 30 years.

Questions

How much interest does this earn in 30 years?

With these inputs the interest is $64,452, on $36,000 paid in, for a final balance of $100,452.

How is compound interest different from simple interest?

Simple interest is paid only on the starting amount. Compound interest is also paid on interest already earned, and on the interest your monthly deposits have earned, which is why the gain accelerates in later years.

How often is the interest added?

This calculator compounds monthly. Many savings accounts compound daily or monthly and funds reinvest continuously; the difference at the same yearly rate is small compared with the effect of time.

Does the result include tax, fees or inflation?

No. It is the plain mathematical result at a fixed rate. Subtract fees and taxes that apply to you, and remember that prices rise too.

Is the rate guaranteed?

Only if it is a fixed-rate product such as a term deposit. Market investments vary from year to year, so use a range of rates to see the spread of outcomes.

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