Lump Sum vs Dollar-Cost Averaging: What 97 Years of Data Say

You have a sum to invest — a bonus, an inheritance, the proceeds of a house sale — and two choices. Put it all into the market today, or feed it in over the next six or twelve months so that a crash next week cannot catch all of it at once. The second option is called dollar-cost averaging (DCA), and it feels like the careful one.

The math is not on its side most of the time. We ran both strategies through every overlapping 12-month window of S&P 500 history from 1926 to mid-2023 — 1,158 of them — and investing everything on day one ended ahead in 69% of them, by 3.4% on average. But the other 31% are not small print. When DCA won, it won by 7.9% on average, and in nearly one window in ten it finished more than 10% ahead.

This guide shows where those numbers come from, what the bad years for a lump sum actually looked like, and how to choose between the two without pretending you can see next year's market.

The setupWhat the two strategies actually do

Take $60,000. Lump sum buys an S&P 500 index fund with all of it on day one. Dollar-cost averaging buys $5,000 on day one and $5,000 on the same day of each of the next eleven months; the money not yet invested waits in cash.

That is the whole difference, and it explains the result before any data comes in. With DCA, on average half the money sits in cash for half a year. Stocks have risen in about 65% of months since 1926, and their long-run return is well above cash. So DCA mostly means holding more cash, for longer, in a market that mostly goes up.

The second line lands close to the 3.4% average gap the historical test found. That is not a coincidence: the gap is mostly the cost of the cash drag, not the result of clever or unlucky timing.

The history97 years of rolling windows

We started a new $1 investment at the beginning of every month from January 1926 and compared the two strategies at the moment the DCA plan finished. Waiting cash earned a flat 3% a year; a second run assumed 0%.

Three patterns hold across every version of the test:

• The longer you spread, the more often you lose. Six months of DCA trails a lump sum in two windows out of three; two years of it trails in three out of four, by 7.4% on average. Stretching the plan is paying more for the same insurance.
• Interest on the waiting cash helps, but not enough. Earning 3% instead of nothing on the uninvested money moves the lump-sum win rate from 74% to 69% for a 12-month plan. In a year of 5% cash rates DCA is cheaper still; it does not become the better bet on average.
• The result is not a relic of the 1930s. Restricting the 12-month test to windows starting in 1990 or later, the lump sum still came out ahead 74% of the time.

Vanguard reached the same shape of answer in its 2023 study, Cost averaging: Invest now or temporarily hold your cash?, across several markets and with a balanced portfolio rather than 100% stocks: investing immediately won roughly two times out of three.

The other 31%What it looks like when DCA wins

Averages hide the distribution, and the distribution is what you live through. Here is how the 1,158 twelve-month windows spread out:

DCA's wins cluster in the same places: the twelve months before a deep bear market. The worst window for a lump sum began in September 1931, when investing everything at once finished 43% behind a monthly plan. More recent ones are easier to picture in dollars:

Notice March 2020. Buying everything at the bottom of the COVID crash was close to perfect timing, and the lump sum still finished slightly behind — because the index level used here is the March average, and the monthly plan kept buying into a market that was only partly recovered. Even near-perfect entries can lose to DCA by a small margin; the big DCA wins all come from years like 2008 and 2022, when the market kept falling after the first purchase.

The choiceHow to decide without predicting the market

If the math favours a lump sum two times out of three, why does DCA survive? Because the question is rarely "which one has the higher expected value". It is "which loss could I live with".

A few practical rules come out of the numbers:

• If you would hold through a 30% drop, the expected-value answer is to invest now. Our best ETFs framework is about choosing what to hold; this is about when, and for long holders the "when" matters less than staying put.
• If you choose DCA, keep it short. Three to six months buys most of the comfort at a fraction of the cost of a 24-month plan.
• Put the waiting cash somewhere that pays. A high-yield savings account or a money market fund narrows the gap; a checking account at 0% widens it.
• Write the schedule down and automate it. A DCA plan that pauses "until things calm down" stops being DCA and becomes market timing — usually at the worst moment.
• Money from every paycheck is a different question. Investing salary as it arrives is not DCA versus a lump sum; it is investing as soon as you have the money, which is what a lump sum is too.

The recordTracking what you actually paid

Whatever you choose, each purchase is a separate buy at its own price. Twelve DCA purchases leave you with twelve lots and an average cost that is neither the first price nor the last.

The Average Buy Price Calculator takes every purchase in a plan and shows the average price you paid against today's price. In the Portfolio Tracker, log each purchase as its own transaction; the tracker keeps the running average cost and gain, so a DCA position and a lump-sum one are measured on the same terms. That record also matters at tax time, as our guide to tracking an investment portfolio explains, and the fund's fee keeps working on every lot either way — expense ratios compound on the whole balance from the day each dollar arrives.

MethodWhere these numbers come from

• Data. Monthly S&P Composite prices and dividends from Robert Shiller's public dataset (econ.yale.edu/~shiller/data.htm), January 1926 to June 2023 — the last month with dividend data in the file. Monthly total return = (price + one month of dividends) ÷ last month's price.
• Strategies. Lump sum invests everything at the start. DCA invests equal amounts at the start of each month, beginning on day one. Waiting cash earns a flat 3% a year (and 0% in the second run).
• Comparison. Both portfolios are valued when the DCA plan finishes. After that they hold the same index, so the proportional gap does not change.
• What it leaves out, and which way it leans. No taxes, fees or trading costs. 100% stocks: a portfolio with bonds has a lower expected return, so the lump-sum edge would be smaller. Shiller's prices are monthly averages, which smooths moves within a month. A flat 3% cash rate understates the 1970s–80s, when cash paid more and DCA cost less, and overstates the 2010s, when it paid almost nothing.

The script that produces every figure here is reproducible from the public file. It is history, not a forecast: the share of up months, and the gap between stocks and cash, could be different over the next ten years. Nothing here is advice about your own money.

FAQLump sum vs dollar-cost averaging

Is lump sum investing better than dollar-cost averaging?

On average, yes. In S&P 500 history since 1926, investing a sum at once beat spreading it over 12 months in about 69% of rolling windows, by 3.4% on average. DCA reduces the damage from a crash in the first year, which is why it can still be the right choice for someone who would otherwise sell in a downturn.

How long should a dollar-cost averaging plan last?

The longer the plan, the more often it loses: 6-month DCA trailed a lump sum in 66% of windows, 12-month in 69%, 24-month in 74%. If you use DCA for peace of mind, three to six months captures most of the protection at the lowest cost.

Does DCA lower my average price?

It gives you the average of the prices on your purchase dates, weighted toward the cheaper ones because a fixed dollar amount buys more shares when prices are low. That average is lower than the simple average of those prices, but not necessarily lower than the price on day one — in a rising market it is usually higher.

What should I do with the cash while I dollar-cost average?

Keep it somewhere that earns interest, such as a high-yield savings account or a money market fund. In our test, earning 3% a year on the waiting cash reduced the lump sum's win rate from 74% to 69% for a 12-month plan.

Is investing every paycheck the same as dollar-cost averaging?

Not in the sense this comparison is about. When money arrives monthly, investing it as it arrives is the immediate option. The lump-sum-versus-DCA question only exists when the whole sum is already in your account.