Compound interest

When what your investments earn starts earning too. The earlier you start, the more this snowball matters.

The 2026 numbers

Numbers checked against the official sources on September 28, 2026.

Understanding why starting early, even small, matters more than the amount.
Seeing the real cost of fees and early withdrawals, which cut the snowball short.

In year one, your investments earn on what you put in. In year two, they also earn on last year’s gains, and so on.
Rule of 72: divide 72 by the yearly return to see how many years it takes to double. At 4.6%, about 15.5 years.
The 4.6% comes from the 2026 projection guidelines (60% stocks, the rest bonds), minus 0.5% in fees. Real returns vary from year to year and can be negative.

$100 a month for 30 years

If your investments earn 4.6% a year:

$100 a month, at 4.6% a yearAfter 30 years: $75,000, of which $36,000 deposited

Your depositsGrowth

After 10 years, growth is still modest ($14,800 for $12,000 deposited). It takes over at the end, which is why starting early matters.

Fictional example, round numbers.

Waiting until you have “enough” to start: the first years are the ones that compound the longest.
Taking gains out along the way: they stop earning.
Underestimating fees: they compound too, against you.
Counting on high, steady returns: real markets come in waves.