How much will $100 a month be worth in 15 years?

Investing $100 a month for 15 years means paying in $18,000 in total. At a hypothetical 7% annual return it would grow to $31,110: $18,000 from your contributions and $13,110 from investment growth. At 4% the balance would be $24,466 ($6,466 of growth), and at 10% it would be $39,844 ($21,844 of growth).

At 4% a year

$24,466

$6,466 of that is growth

At 7% a year

$31,110

$13,110 of that is growth

At 10% a year

$39,844

$21,844 of that is growth

4%, 7% and 10% are example rates, not forecasts. Real returns change from year to year and are never guaranteed, and these figures leave out fees, taxes and inflation.

$100 a month for 15 years at different rates of return

Annual return	Final balance	Total contributed	Interest earned
1%	$19,405	$18,000	$1,405
2%	$20,942	$18,000	$2,942
3%	$22,624	$18,000	$4,624
4%	$24,466	$18,000	$6,466
5%	$26,482	$18,000	$8,482
6%	$28,691	$18,000	$10,691
7%	$31,110	$18,000	$13,110
8%	$33,761	$18,000	$15,761
9%	$36,664	$18,000	$18,664
10%	$39,844	$18,000	$21,844
11%	$43,329	$18,000	$25,329
12%	$47,146	$18,000	$29,146

Assumes no starting balance, a contribution at the end of every month, and a constant rate compounded once a year (an effective annual rate). You pay in $18,000 in every row; only the growth changes, from $1,405 at 1% to $29,146 at 12%.

Try your own numbers

The calculator starts with this example at 7%. Change the amount, rate or time period, add a starting balance, or switch the compounding, and the result updates as you type.

Balance after 15 years

$31,110

42.1% of that is interest. Your balance is 1.73 times what you put in.

Total contributions

$18,000

Interest earned

$13,110

Growth by year

Contributions
Interest

Year-by-year breakdown

Year	Contributions	Interest	Balance
1	$1,200	$38	$1,238
2	$2,400	$163	$2,563
3	$3,600	$380	$3,980
4	$4,800	$697	$5,497
5	$6,000	$1,120	$7,120
6	$7,200	$1,656	$8,856
7	$8,400	$2,314	$10,714
8	$9,600	$3,102	$12,702
9	$10,800	$4,029	$14,829
10	$12,000	$5,105	$17,105
11	$13,200	$6,341	$19,541
12	$14,400	$7,746	$22,146
13	$15,600	$9,335	$24,935
14	$16,800	$11,118	$27,918
15	$18,000	$13,110	$31,110

How much is your money and how much is growth?

At 7%, 15 years is not long enough for growth to overtake what you pay in: growth is 42% of the final balance and the other 58% is your own money. Keep contributing at the same pace and growth would pass contributions during year 19. The rate matters a lot here: growth overtakes contributions in year 14 at 10%, while at 4% it would take until year 33, after this 15-year period ends.

In year 15 alone, the balance earns $1,992 at 7%. That is more than the $1,200 you add that year, and compares with $38 of growth in year 1.

What if you change the plan?

Each row changes one thing and keeps everything else the same, at the 7% example rate. The comparison is with $100 a month for 15 years, which ends at $31,110.

Change	Final balance	Difference
Keep contributing for 5 more years (20 years in total)	$50,754	+$19,643
Start 5 years later (contribute for 10 years)	$17,105	−$14,005
Contribute $200 a month instead of $100	$62,221	+$31,110
Start with $10,000 already invested	$58,701	+$27,590
Contribute at the start of each month instead of the end	$31,286	+$176
Earn 6% a year instead of 7%	$28,691	−$2,419

Starting 5 years later means paying in $6,000 less, but the final balance is $14,005 lower. The gap is bigger than the missing contributions because the earliest payments are the ones with the longest time to grow. A return that is one point lower leaves you with $2,419 less after 15 years, which is roughly what a 1% annual fee would cost.

Working backwards: to reach $50,000 in 15 years at 7%, starting from zero, you would need to invest about $161 a month.

When would the balance reach $50,000?

The table shows the year in which the balance first reaches each amount, assuming the same $100 a month continues for as long as it takes. Years in bold fall within this page's 15-year period.

Balance reaches	At 4%	At 7%	At 10%
$2,500	Year 3	Year 2	Year 2
$5,000	Year 4	Year 4	Year 4
$10,000	Year 8	Year 7	Year 7
$25,000	Year 16	Year 14	Year 12
$50,000	Year 25	Year 20	Year 17

How this is calculated

The rate is treated as an effective annual rate, so the balance grows by exactly 7% over a full year. The monthly rate that compounds to 7% a year is:

Monthly rate = (1 + 0.07)^1/12 − 1 = 0.5654%

With $100 added at the end of each month for 180 months (15 × 12), the contributions grow to:

Balance = 100 × [1.005654¹⁸⁰ − 1] ÷ 0.005654 ≈ $31,110

The rates shown here are rounded; the result uses full precision. Of that balance, 100 × 180 = $18,000 is your contributions and the remaining $13,110 is growth. Every other row in the rate table uses the same formula with a different annual rate. The compound interest calculator page explains the formulas in more detail.

Frequently asked questions

How much interest will $100 a month earn in 15 years?

It depends on the rate of return. At a constant 7% a year, $100 a month for 15 years earns $13,110 on top of $18,000 in contributions, for a balance of $31,110. At 4% the growth is $6,466, and at 10% it is $21,844. These rates are examples, not predictions.

How long does it take to reach $50,000 investing $100 a month?

With a constant 7% annual return and no starting balance, the balance passes $50,000 during year 20. For comparison, at 10% it takes until year 17, and at 4% it takes until year 25.

How much do I need to invest each month to have $50,000 in 15 years?

At a constant 7% annual return you would need about $161 a month for 15 years, starting from zero. At 4% you would need about $204 a month, and at 10% about $125 a month.

$100 a month over other periods

Other monthly amounts for 15 years

A single lump sum for 15 years

See all compound interest examples in one table, or start from scratch with the compound interest calculator.