How much will $300 a month be worth in 15 years?

Investing $300 a month for 15 years means paying in $54,000 in total. At a hypothetical 7% annual return it would grow to $93,331: $54,000 from your contributions and $39,331 from investment growth. At 4% the balance would be $73,397 ($19,397 of growth), and at 10% it would be $119,533 ($65,533 of growth).

At 4% a year

$73,397

$19,397 of that is growth

At 7% a year

$93,331

$39,331 of that is growth

At 10% a year

$119,533

$65,533 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.

$300 a month for 15 years at different rates of return

Annual return	Final balance	Total contributed	Interest earned
1%	$58,214	$54,000	$4,214
2%	$62,825	$54,000	$8,825
3%	$67,872	$54,000	$13,872
4%	$73,397	$54,000	$19,397
5%	$79,447	$54,000	$25,447
6%	$86,074	$54,000	$32,074
7%	$93,331	$54,000	$39,331
8%	$101,282	$54,000	$47,282
9%	$109,992	$54,000	$55,992
10%	$119,533	$54,000	$65,533
11%	$129,986	$54,000	$75,986
12%	$141,437	$54,000	$87,437

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 $54,000 in every row; only the growth changes, from $4,214 at 1% to $87,437 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

$93,331

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

Total contributions

$54,000

Interest earned

$39,331

Growth by year

Contributions
Interest

Year-by-year breakdown

Year	Contributions	Interest	Balance
1	$3,600	$114	$3,714
2	$7,200	$488	$7,688
3	$10,800	$1,140	$11,940
4	$14,400	$2,090	$16,490
5	$18,000	$3,359	$21,359
6	$21,600	$4,968	$26,568
7	$25,200	$6,942	$32,142
8	$28,800	$9,306	$38,106
9	$32,400	$12,087	$44,487
10	$36,000	$15,316	$51,316
11	$39,600	$19,022	$58,622
12	$43,200	$23,239	$66,439
13	$46,800	$28,004	$74,804
14	$50,400	$33,355	$83,755
15	$54,000	$39,331	$93,331

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 $5,977 at 7%. That is more than the $3,600 you add that year, and compares with $114 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 $300 a month for 15 years, which ends at $93,331.

Change	Final balance	Difference
Keep contributing for 5 more years (20 years in total)	$152,261	+$58,929
Start 5 years later (contribute for 10 years)	$51,316	−$42,016
Contribute $400 a month instead of $300	$124,442	+$31,110
Start with $10,000 already invested	$120,922	+$27,590
Contribute at the start of each month instead of the end	$93,859	+$528
Earn 6% a year instead of 7%	$86,074	−$7,258

Starting 5 years later means paying in $18,000 less, but the final balance is $42,016 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 $7,258 less after 15 years, which is roughly what a 1% annual fee would cost.

Working backwards: to reach $250,000 in 15 years at 7%, starting from zero, you would need to invest about $804 a month.

When would the balance reach $250,000?

The table shows the year in which the balance first reaches each amount, assuming the same $300 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%
$10,000	Year 3	Year 3	Year 3
$25,000	Year 7	Year 6	Year 6
$50,000	Year 12	Year 10	Year 9
$100,000	Year 19	Year 16	Year 14
$250,000	Year 34	Year 26	Year 22

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 $300 added at the end of each month for 180 months (15 × 12), the contributions grow to:

Balance = 300 × [1.005654¹⁸⁰ − 1] ÷ 0.005654 ≈ $93,331

The rates shown here are rounded; the result uses full precision. Of that balance, 300 × 180 = $54,000 is your contributions and the remaining $39,331 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 $300 a month earn in 15 years?

It depends on the rate of return. At a constant 7% a year, $300 a month for 15 years earns $39,331 on top of $54,000 in contributions, for a balance of $93,331. At 4% the growth is $19,397, and at 10% it is $65,533. These rates are examples, not predictions.

How long does it take to reach $250,000 investing $300 a month?

With a constant 7% annual return and no starting balance, the balance passes $250,000 during year 26. For comparison, at 10% it takes until year 22, and at 4% it takes until year 34.

How much do I need to invest each month to have $250,000 in 15 years?

At a constant 7% annual return you would need about $804 a month for 15 years, starting from zero. At 4% you would need about $1,022 a month, and at 10% about $627 a month.

$300 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.