Dollar-Cost Averaging Explained: What the Research Says

Dollar-cost averaging (DCA) means investing a fixed dollar amount at regular intervals, such as every month, regardless of the price. Because the same dollars buy more shares when prices are low and fewer when prices are high, your average cost per share ends up below the simple average of the prices you paid.

In short: dollar-cost averaging is a good habit when you invest from each paycheque, because that is simply how money arrives. When you already have a lump sum, the research is clear that investing it all at once has usually come out ahead, roughly two-thirds of the time in historical tests, because markets have tended to rise more often than not. Spreading the lump sum out mainly buys emotional comfort, at an expected cost.

Two different situations with the same name

The term gets used for two different decisions, and it helps to separate them:

Investing as you earn. You put $500 from every paycheque into a 401(k), RRSP, or TFSA. There is no lump sum to compare against; you are investing money as soon as you have it. This is often called DCA, and it is a sound habit.
Spreading out a lump sum. You have $60,000 from an inheritance, bonus, or sale and must decide whether to invest it today or in pieces over the next several months. This is the decision most research on DCA is about.

Vanguard’s 2023 research paper makes the same distinction and focuses on the second case.

Why the paycheque case is different

If your money arrives monthly, there is no lump sum sitting in cash and no choice to make between “now” and “later”: investing each amount as soon as it arrives already maximizes your time in the market, which is the same principle that favours lump sums. Automatic contributions to a workplace plan or a pre-authorized purchase plan also take the decision out of your hands each month, which removes the temptation to wait for a better price. The rest of this article is about the harder question, what to do with money you already have.

The arithmetic: why your average cost is lower

Suppose you invest $400 a month for three months in a fund whose price moves like this:

Month	Price	Shares bought with $400
1	$10.00	40.00
2	$8.00	50.00
3	$12.00	33.33
Total		123.33 shares for $1,200

The simple average of the three prices is ($10 + $8 + $12) ÷ 3 = $10.00. Your average cost per share is $1,200 ÷ 123.33 = $9.73.

That happens every time prices vary: a fixed dollar amount automatically buys more when the price is low. (Mathematically, your average cost is the harmonic mean of the prices, which is always at or below the ordinary average.) This is the part of DCA that is true and genuinely useful.

The comparison that matters: versus investing all at once

A lower average cost than the average price is not the same as a better result than investing everything on day one. Compare both approaches in two scenarios. In each, you have $1,200 at the start.

Scenario A: the price dips, then recovers

Same prices as above: $10, $8, $12. The price ends at $12.

Lump sum: $1,200 ÷ $10 = 120 shares, worth 120 × $12 = $1,440.
DCA: 123.33 shares, worth 123.33 × $12 = $1,480.

DCA wins by $40 because it bought some shares during the dip.

Scenario B: the price rises steadily

Prices are $10, $11, $12.

Lump sum: 120 shares at $10, worth 120 × $12 = $1,440.
DCA: 40.00 + 36.36 + 33.33 = 109.70 shares, worth 109.70 × $12 = $1,316.

Lump sum wins by $124, because the money that waited bought at higher prices.

So the question becomes: historically, how often have markets looked like Scenario A, and how often like Scenario B?

What the research says

Vanguard, 2023

In Cost averaging: Invest now or temporarily hold your cash? (Vanguard research, February 2023), Megan Finlay and Josef Zorn compared investing a lump sum immediately with splitting it into three equal parts invested a month apart. They measured wealth after one year, on a rolling basis, using MSCI World Index returns from 1976 to 2022 for a 100% stock portfolio.

According to the paper:

Lump sum beat cost averaging 68% of the time.
Cost averaging still beat staying entirely in cash 69% of the time.
When the uninvested cash was assumed to earn interest at the 3-month US Treasury bill rate, lump sum still won 65% of the time.
For a 60% stock / 40% bond portfolio starting at $100,000, the average ending value after one year was $109,360 for lump sum versus $107,453 for three-month cost averaging, about 1.8% more.
Spreading the money over more months (four, five, six) generally made cost averaging look worse, not better.

The paper reports similar results across regions. For Canada, using the S&P/TSX Composite from 1985 to 2022, lump sum beat three-month cost averaging 67.2% of the time.

Vanguard, 2012

An earlier Vanguard paper, Dollar-cost averaging just means taking risk later (2012) by Anatoly Shtekhman, Christos Tasopoulos and Brian Wimmer, tested a 12-month DCA schedule in the US, the UK and Australia and reached the same conclusion: lump-sum investing came out ahead about two-thirds of the time. The title states the reasoning plainly. DCA does not avoid market risk; it postpones taking it.

Why the result keeps showing up

The explanation is simple. Over most historical periods, stocks have earned more than cash. Money waiting on the sidelines misses that extra return, which economists call the risk premium. The Vanguard 2023 paper notes that from 1976 to 2022, US stocks beat cash, proxied by Treasury bills, in 76% of the periods it measured. DCA keeps part of your money out of the market for longer, so on average it earns less. Neither paper’s results are a forecast; they describe what happened in the historical data tested.

The honest trade-offs

If lump sum usually wins, why would anyone dollar-cost average a windfall? Because “usually” is not “always,” and the times it loses can be painful.

What DCA gives you:

Less regret. Investing $60,000 the week before a 20% decline feels terrible. DCA reduces the chance that your entire sum goes in at a peak. The Vanguard 2023 paper says that for investors with very high aversion to losses, cost averaging may be a reasonable choice if the alternative is holding cash indefinitely.
A plan you can stick to. If the fear of a bad entry point would otherwise keep the money in cash for years, a fixed schedule gets it invested. Cost averaging beat cash 69% of the time in the Vanguard data.
Lower risk during the transition. While part of the money is still in cash, the portfolio is less exposed to a decline.

What DCA costs you:

Lower expected return, roughly a percentage point or two over the transition in the Vanguard tests, more if the schedule is long.
More decisions. Every scheduled purchase is a chance to second-guess, pause, or “wait for a dip” that may not come.
Possibly more trading costs, if your broker charges commissions on each purchase.

A middle ground some people choose: invest a large part immediately and spread the rest over a few months, on a fixed schedule set in advance.

What can go wrong

Turning DCA into market timing. The plan only works as designed if you stick to the schedule. Skipping purchases when the news is bad, or speeding up when markets are hot, turns a rule into guessing. See investor behavior mistakes.
Very long schedules. Spreading a lump sum over two or three years leaves a lot of money in cash for a long time. The research above suggests the longer the schedule, the larger the expected shortfall.
Assuming DCA protects you from losses. It does not. If the market falls for the whole period and beyond, both lump sum and DCA lose money. DCA just loses a bit less early on. History has had long declines; see bull and bear markets.
Registered-account timing in Canada and the US. Contribution room and deadlines (RRSP, TFSA, IRA, 401(k)) set their own limits on when money can go in. Spreading contributions out does not change those limits; see Canadian registered accounts explained.
Fees per purchase. A fixed commission on small, frequent buys can eat a meaningful share of each amount. Commission-free trading and fractional shares at many brokers have reduced this problem but not removed it everywhere (see how stock brokers make money).

The short version

Investing a fixed amount on a schedule lowers your average cost per share relative to the average price, and it is the natural way to invest money from each paycheque. For a lump sum, historical research, including Vanguard’s 2023 study across global markets and Canada, found that investing all at once beat spreading it out about two-thirds of the time, because markets have usually risen while cash waited. DCA’s real value is behavioural: it can help you get invested and stay invested. Weigh that against its expected cost, decide in advance, and stick to the schedule.