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Investment growth by amount (7% average return)

By Jonathan Pimperton, ACA-qualified accountant Published

What regular monthly investing and one-off lump sums actually become over 10, 20, and 30 years at a 7% average annual return, compounded monthly — every figure computed, not estimated.

Monthly investing

Starting from zero and investing the same amount every month, at a 7% annual return compounded monthly with contributions at the end of each month:

Monthly amount 10 years 20 years 30 years
$100/month $17,308 $52,093 $121,997
$200/month $34,617 $104,185 $243,994
$250/month $43,271 $130,232 $304,993
$500/month $86,542 $260,463 $609,985
$1,000/month $173,085 $520,927 $1,219,971
$2,000/month $346,170 $1,041,853 $2,439,942

The long timeframes do most of the work: invest $500 a month for 30 years and you deposit $180,000 in total — compounding adds another $429,985, for a final balance of $609,985. That means 70% of the end result is growth, not deposits.

Figures are shown in dollars, but the maths is currency-agnostic — read them as pounds or euros and every number is identical.

Lump sums

A one-off amount invested once and left alone — no further contributions — at the same 7% annual return compounded monthly:

Lump sum 10 years 20 years 30 years
$5,000 $10,048 $20,194 $40,582
$10,000 $20,097 $40,387 $81,165
$25,000 $50,242 $100,968 $202,912
$50,000 $100,483 $201,937 $405,825
$100,000 $200,966 $403,874 $811,650
$500,000 $1,004,831 $2,019,369 $4,058,249

At 7% compounded monthly, a lump sum roughly doubles every decade: $100,000 left untouched becomes $200,966 in 10 years, $403,874 in 20, and $811,650 in 30 — a 8.1× multiple without a single further deposit.

The assumptions behind these numbers

Why 7%?

7% is a planning figure for long-run equity returns before inflation. Broad, diversified stock index funds have historically averaged around 7–10% a year nominal over multi-decade periods, so 7% sits at the cautious end — leaving some margin for fund fees and imperfect timing. It is an assumption, not a promise: change it in the calculator below and watch how sensitive the 30-year numbers are.

Real returns are not a smooth line

No portfolio grows by 0.58% every month. The 7% average is built from years that gain 20% and years that lose 20%, and your actual balance will swing well above and below these curves along the way. Over 10+ year horizons the average tends to reassert itself, but over any single year these tables say nothing about what will happen.

Inflation eats purchasing power

These are nominal figures. At 2–3% inflation, prices roughly double over 30 years — so a $811,650 balance in 2056 buys closer to what half that amount buys today. To translate a future balance into today’s money, run it through the inflation calculator.

Currency doesn’t change the maths

Compounding is unit-free: £500 a month at 7% produces exactly the same numbers as $500 a month at 7%. Use whichever currency you think in.

Run your own numbers

Your starting balance, your monthly amount, your return assumption — with a year-by-year table and the contributions/growth split, right here.

Inputs

Display currency

Amount you're starting with today

$
$0$500K

Amount you'll add each month

$
$0$5K

~4-5% for savings accounts, ~7-10% for stock market index funds

%

How long you'll let it grow

Final Balance

$144,573

After 20 years of compounding at 7% annually

Total Contributions

$58,000

Total Interest Earned

$86,573

Growth Over Time

Interest overtakes deposits — Yr 16

Year-by-Year Breakdown

YearBalance

Start growing your money

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