Dollar-cost averaging vs lump sum investing

Dollar-cost averaging vs lump sum investing: how each works, what Vanguard's research found, and why spreading out can still make sense. With a calculator.

Part of the Investing Foundations track on Agenticks. About 10 minutes, written for a beginner reader.

Read first: Compounding and why time horizon matters, Risk and return, the basic tradeoff.

Last reviewed .

Risk notice. Backtested and hypothetical results are simulated: no trades were placed, the rules were applied to past data with the benefit of hindsight, and they may not reflect liquidity, slippage or every cost. Past results, real or simulated, do not predict future results.

Key takeaways

Dollar-cost averaging means investing the same amount of money at regular intervals, whatever the market is doing. In the UK it is often called pound-cost averaging. The idea shows up in two quite different situations, and mixing them up causes most of the confusion around it. The first is everyday investing. If you put part of each paycheque into the market as it arrives, you are dollar-cost averaging by default, because there is no pile of money waiting. Investing each amount when you have it is the natural thing to do. The second is a windfall: an inheritance, a bonus, the sale of a house or business. Now the money already exists, and there is a real choice. Invest it all at once, called lump sum investing, or feed it in over several months? The research below is about this second situation.

The mechanical appeal of dollar-cost averaging is simple. A fixed amount buys more shares when the price is low and fewer when it is high, so your average cost per share ends up below the average of the prices you paid. Here is that arithmetic with three made-up months.

Worked example: $300 a month at three different prices

You invest $300 at the start of each month. The price moves from $10 to $7.50 to $12.

Month 1 at $10.00 (300 / 10.00)30 shares
Month 2 at $7.50 (300 / 7.50)40 shares
Month 3 at $12.00 (300 / 12.00)25 shares
Total invested$900 for 95 shares
Average of the three prices ((10 + 7.50 + 12) / 3)$9.83
Your average cost per share (900 / 95)about $9.47
Value at $12 after month 3$1,140

Illustrative prices. Had all $900 gone in at $10 in month 1, it would have bought 90 shares worth $1,080. Here spreading won because the price dipped first.

That example flatters spreading, because the price happened to dip in the middle. If the price had climbed steadily from $10 to $11 to $12 instead, the lump sum would have bought everything at the lowest price of the three and come out ahead. Whether spreading helps depends entirely on the path prices take, and nobody knows that path in advance.

So which has usually worked better with a lump sum in hand? A 2023 Vanguard study tested exactly that. It compared investing a lump sum at once with splitting it into three equal parts invested a month apart, measured over rolling one-year periods using global stock market returns from 1976 to 2022, with no interest earned on the cash waiting to be invested. Investing the lump sum straight away came out ahead about 68% of the time. Spreading it out still beat simply keeping the money in cash about 69% of the time. The authors report similar results in the US, the UK, Canada, Australia and Europe. The reason is not mysterious. Over those decades markets rose more often than they fell, so any money held back in cash usually missed some growth. Spreading a lump sum out is, in effect, choosing to hold more cash for a while. That is the same compounding idea from earlier in this track: money starts growing only once it is invested. As always, these are historical results and past returns do not guarantee future returns.

How much does the choice matter? In the same study, for $100,000 in an all-stock portfolio, the median result after one year was about 2.2% higher with the lump sum. For a portfolio of 40% stocks and 60% bonds the median advantage shrank to about 1.2%, because less of the waiting money was missing out on stock market growth. Paying interest on the waiting cash narrowed the gap without closing it: with a Treasury bill rate on the cash, the lump sum still came out ahead about 65% of the time for the all-stock portfolio. The picture flips in the worst outcomes. In the bottom 5% of one-year periods for the all-stock portfolio, the lump sum finished at about $82,900 and the spread approach at about $85,900. That is the whole trade in two numbers: a better typical result for investing at once, a softer landing in the bad cases for spreading out.

Spreading changes when you take the risk, not how much

Once the last slice is invested, both approaches own the same thing and carry the same risk. Spreading only changes when the money goes in, and the waiting money has usually cost more in missed growth than it saved in avoided falls.

That does not make spreading foolish. Two out of three is not every time, and the one time in three can hurt. Putting a large sum in the week before a sharp fall is painful, and the fear of doing exactly that keeps many people sitting in cash for years, which the research suggests is the worst of the three choices. The Vanguard authors note that cost averaging can suit investors with a very high aversion to risk and losses, because it limits the damage from a fall soon after investing and the regret that comes with it, helping them stay committed to the plan. That links back to risk tolerance and capacity: a plan you can follow beats a better plan you abandon. The same study found that the longer the spreading period, the larger the expected cost compared with a lump sum. So a spreading plan that stretches on, or turns into waiting for a better moment that never seems to arrive, gives up the most. Writing the schedule down in advance is one way people keep it short.

For regular savers, none of this argues against the habit. Investing a set amount every month means the decision of when to invest is made once, in advance, and does not have to be made again in every scary headline. It keeps money going in through falls, when each fixed contribution buys more units than it did before, and Investor.gov describes that steady pattern of adding new money as one way to manage risk over a long period. The lump sum question only appears when a large amount is already sitting in cash.

Lump sum or spread it out

This uses one made-up price path that grows at a steady assumed rate, 5% a year by default, which is an assumption and not a forecast. The one-time price move is a shock: it jolts the price up or down by the percentage you choose, once, in the month you choose. Uninvested cash earns nothing. With the defaults and no shock, the lump sum ends 24 months later at about $13,259 against about $12,961 for spreading over 12 months. Now set the move to -30% in month 3: spreading wins, about $11,971 against $9,282, because most of its money buys after the fall. Then move the same fall to month 20, after the spreading has finished, and see which comes out ahead.

Which situation does the lump sum versus spreading research actually address? Deciding how to invest a windfall you already have The study compares investing money in hand all at once with feeding it in over a few months.

You can weigh a lump sum against averaging

You know how dollar-cost averaging works, why lump sums have tended to come out ahead on average, and why some people spread money out anyway.

Check your understanding

Why has investing a lump sum all at once tended to beat spreading it out?
Markets have risen more often than they have fallen, so money left in cash usually missed some growth. Spreading keeps part of the money uninvested for longer, and over the periods studied that time out of the market usually cost more than it saved.
In the worked example, $300 a month buys at $10, $7.50 and $12. Why is the average cost per share lower than the average price?
A fixed amount buys more shares when the price is low and fewer when it is high. The $7.50 month bought 40 shares and the $12 month only 25, which pulls the average cost down to about $9.47.
In the calculator, you set a one-time price move of -30% in month 3 and the spread approach finishes ahead. Why?
Most of the spread money was still uninvested when the price fell, so it bought in afterwards at lower prices. The lump sum took the whole fall. The spread put only three slices in before it and the rest at the lower price.
Someone invests part of every paycheque as soon as it arrives. Which statement fits?
There is no lump sum to compare, so investing each amount as it arrives is the natural way to do it. The lump sum research is about money you already have. Regular contributions are simply money being invested when it exists.

Common questions

What is dollar-cost averaging?
Dollar-cost averaging means investing the same amount at regular intervals, whatever the market is doing. A fixed amount buys more units when prices are low and fewer when they are high. In the UK it is often called pound-cost averaging.
Is it better to invest a lump sum or dollar-cost average?
Vanguard's 2023 research found that investing a lump sum at once beat spreading it over three months about 68% of the time, using global stock data from 1976 to 2022. Spreading out still beat holding cash most of the time, and it lowers the risk of investing everything just before a fall.
Does dollar-cost averaging reduce risk?
It reduces the risk of putting all your money in at a bad moment, because the money goes in gradually. The trade-off is that the uninvested part misses any growth while it waits, which is why it has tended to finish behind a lump sum on average.

Terms defined in this lesson

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Agenticks Learn is general education. It is not financial, investment, tax or legal advice, it does not take your situation into account, and nothing on it is a recommendation to buy, sell or hold any security or to open any account. Examples use illustrative numbers. Investing involves risk, including losing money you put in, and past performance does not predict future results. Tax rules and limits change; the official sources linked in each lesson are the final word.