Returns that earn returns
The engine is compounding. In year one your money earns a return. In year two, that return earns a return too — and so does every year after. Your gains start generating their own gains. Early on the effect is tiny; given enough time it becomes the largest part of your wealth. Regulators build free compound-interest calculators for exactly this reason.[1]
The maths, with a simple example
Invest 100 a month and leave it alone. At a 9% average annual return, you contribute 1,200 a year — 30,000 over 25 years. But the balance grows to roughly 105,000. More than 70% of the final amount is growth you never deposited. That gap is the snowball.
The Rule of 72
A quick mental shortcut: divide 72 by your annual return to estimate how many years it takes your money to double. At 9%, roughly 72 ÷ 9 = 8 years to double, then double again, and again. Doubling repeatedly is why the later milestones arrive so much faster than the first.
Why the first 10K is the hard one
At the start, almost everything in your account is money you put in — the snowball is small and barely rolling. As it grows, growth does more of the lifting than your deposits. That is why the jump from 500K to 1M usually takes far less time than the crawl from 0 to 10K. Run your own numbers and watch the gap.
Time beats timing
Because compounding needs time more than it needs large sums, starting early with a modest monthly amount often beats starting later with much more. The evidence backs the “stay invested” approach: over 125 years global equities compounded to roughly 5% a year after inflation, but almost all of that came to investors who stayed in through the bad years, not those who tried to jump in and out.[2] The most valuable thing you can give your snowball is years.
What melts the snowball
Two things shrink it: time out of the market and fees. A fee is charged on your whole balance every year, so it grows exactly as fast as your snowball does — quietly melting a slice off the top for decades. Because the cost compounds against you, Morningstar finds low fees are the most reliable predictor of better long-run outcomes.[3] Keeping fees low is the one return factor you fully control. See the effect for yourself.
Common questions
What is the snowball effect in investing?
It is compound growth: the returns your investments earn go on to earn returns themselves. Over time the growth compounds on previous growth, so wealth accelerates the longer you stay invested.
How long does it take to double my money?
Use the Rule of 72: divide 72 by your annual return. At an 8% return that is about 9 years to double. Higher returns double faster, but also carry more risk.
Is it better to invest a lump sum or monthly?
Both benefit from compounding. Investing monthly (sometimes called cost averaging) is how most people build wealth from income, and starting early matters more than the amount. What compounding rewards above all is time in the market.
Do fees really matter that much?
Yes. Because a percentage fee is charged on your entire balance every year, it compounds against you. Over decades a 1.5% fee versus 0.1% can cost a large share of your final pot — try the fee tool to see the number for your own contributions.