Dollar-Cost Averaging vs Lump Sum: What 75 Years of Data Shows
By Lucian — builder & engineer, LK Forge
You've come into a sum of money and you want it in the market. Do you invest it all at once, or feed it in gradually — dollar-cost averaging — to avoid buying right before a crash? It's one of investing's oldest arguments, and it's answerable with data. We ran it against every starting month of the S&P 500 from 1950 to 2025: deploy the whole amount now, or spread it evenly over the next few months, and see which ended up ahead.
· 6 min read · every number from a re-runnable script
The Numbers
The longer you spread it, the more often the lump wins
The reason is mundane: the market goes up more often than it goes down, so money sitting on the sidelines waiting to be invested is money missing the average day's gain. Spread the same amount over two years instead of one and you leave even more of it out of the market for longer, which is why the lump-sum win rate climbs from 76.2% to 82.7%. On a concrete $10,000 deployed over a year, the lump sum ended ahead by $607 on average — not a fortune, but a consistent one.
When Dollar-Cost Averaging Wins
Averages hide the interesting part. Dollar-cost averaging lost the typical year — but when it won, it won for one reason: the market fell right after you started. Sort every one-year period by how much DCA beat the lump sum, and the top of the list isn't scattered across history. It bunches up in one place: August 2008, on the eve of the 2008 financial crisis, was the single best month to have been feeding money in slowly rather than all at once — dollar-cost averaging finished about 30.8 points ahead, because each later purchase bought in cheaper as the market collapsed. The runners-up are the other months of 2007 and 2008.
That's the honest way to read this: dollar-cost averaging is not a way to earn more, it's a way to be wrong by less when your timing is unlucky. You're trading a bit of expected return — that $607 on $10,000 — for protection against the one scenario everyone fears, putting it all in at the top. Whether that trade is worth it is about temperament, not math. If spreading it in is what lets you actually invest the money instead of sitting in cash for a year, the expected-return cost is cheap for the peace of mind — and cash on the sidelines has its own, larger, cost.
How We Measured It
The comparison is deliberately like-for-like. Both strategies invest the same total. The lump sum goes in at month zero; the dollar-cost-averaging version splits it into equal monthly buys across the window, and we compare the two at the end of that window, when both are fully invested. We use S&P 500 total return — dividends reinvested — because that's what a real index fund earns, and we assume the not-yet-invested DCA cash earns nothing, which is the conservative, common assumption. Every ending value is a real historical outcome, run for every start month from 1950 to 2025, then tallied.
- Data: the monthly S&P 500 total-return index (base 100, 1950–2025) built into the Dollar-Cost Averaging Calculator — the Shiller monthly series scaled so each year matches the official S&P Dow Jones Indices annual return.
- Method: for every start month, lump = amount × index[end] ÷ index[start]; DCA = the same amount split evenly across the window, each buy grown to the end; win = higher ending value.
- Check any single case yourself: the two calculators below show the lump-sum and DCA outcome for any period you pick, so you can spot-check the historical numbers behind this study.
A note on scope: this is the classic "deploy a windfall now vs later" question, not regular saving from a paycheck — if you're investing each month as you earn it, you're already dollar-cost averaging by necessity, and there's no lump sum to compare against. Past performance doesn't predict the future; this is history, not advice.
Run Your Own Numbers
Both free, both in your browser — no sign-up. See what any amount would have done, lump sum or averaged in.