How much will $100 a month be worth in 20 years?

Investing $100 a month for 20 years means paying in $24,000 in total. At a hypothetical 7% annual return it would grow to $50,754: $24,000 from your contributions and $26,754 from investment growth. At 4% the balance would be $36,384 ($12,384 of growth), and at 10% it would be $71,826 ($47,826 of growth).

At 4% a year

$36,384

$12,384 of that is growth

At 7% a year

$50,754

$26,754 of that is growth

At 10% a year

$71,826

$47,826 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 20 years at different rates of return

Annual return	Final balance	Total contributed	Interest earned
1%	$26,544	$24,000	$2,544
2%	$29,423	$24,000	$5,423
3%	$32,685	$24,000	$8,685
4%	$36,384	$24,000	$12,384
5%	$40,580	$24,000	$16,580
6%	$45,344	$24,000	$21,344
7%	$50,754	$24,000	$26,754
8%	$56,900	$24,000	$32,900
9%	$63,885	$24,000	$39,885
10%	$71,826	$24,000	$47,826
11%	$80,854	$24,000	$56,854
12%	$91,121	$24,000	$67,121

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 $24,000 in every row; only the growth changes, from $2,544 at 1% to $67,121 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 20 years

$50,754

52.7% of that is interest. Your balance is 2.11 times what you put in.

Total contributions

$24,000

Interest earned

$26,754

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
16	$19,200	$15,326	$34,526
17	$20,400	$17,781	$38,181
18	$21,600	$20,492	$42,092
19	$22,800	$23,476	$46,276
20	$24,000	$26,754	$50,754

How much is your money and how much is growth?

At 7%, most of the balance is money you paid in for the first 18 years. During year 19, total growth passes total contributions, and by the end of year 20 growth makes up 53% of the balance. 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 20-year period ends.

In year 20 alone, the balance earns $3,277 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 20 years, which ends at $50,754.

Change	Final balance	Difference
Keep contributing for 5 more years (25 years in total)	$78,304	+$27,551
Start 5 years later (contribute for 15 years)	$31,110	−$19,643
Contribute $200 a month instead of $100	$101,507	+$50,754
Start with $10,000 already invested	$89,450	+$38,697
Contribute at the start of each month instead of the end	$51,041	+$287
Earn 6% a year instead of 7%	$45,344	−$5,410

Starting 5 years later means paying in $6,000 less, but the final balance is $19,643 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 $5,410 less after 20 years, which is roughly what a 1% annual fee would cost.

Working backwards: to reach $100,000 in 20 years at 7%, starting from zero, you would need to invest about $197 a month.

When would the balance reach $100,000?

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 20-year period.

Balance reaches	At 4%	At 7%	At 10%
$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
$100,000	Year 38	Year 29	Year 24

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 240 months (20 × 12), the contributions grow to:

Balance = 100 × [1.005654²⁴⁰ − 1] ÷ 0.005654 ≈ $50,754

The rates shown here are rounded; the result uses full precision. Of that balance, 100 × 240 = $24,000 is your contributions and the remaining $26,754 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 20 years?

It depends on the rate of return. At a constant 7% a year, $100 a month for 20 years earns $26,754 on top of $24,000 in contributions, for a balance of $50,754. At 4% the growth is $12,384, and at 10% it is $47,826. These rates are examples, not predictions.

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

With a constant 7% annual return and no starting balance, the balance passes $100,000 during year 29. For comparison, at 10% it takes until year 24, and at 4% it takes until year 38.

How much do I need to invest each month to have $100,000 in 20 years?

At a constant 7% annual return you would need about $197 a month for 20 years, starting from zero. At 4% you would need about $275 a month, and at 10% about $139 a month.

$100 a month over other periods

Other monthly amounts for 20 years

A single lump sum for 20 years

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