Research Library · Study 13
Lump Sum vs Pound-Cost Averaging: What Vanguard’s Research Found
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Overview
If you have a sum to invest, such as savings, an inheritance or a bonus, you can put it all in at once (a lump sum) or spread it over several months (pound-cost averaging, called dollar-cost averaging in the US). So which wins, lump sum vs pound cost averaging? Vanguard tested both across decades of data.
- Timeframe
- A one-off decision, then years of holding
- Markets
- Diversified share and bond funds
- Difficulty
- Beginner
Two ways to invest a sum
Lump sum: invest everything on day one.
Pound-cost averaging: split the money into equal parts and invest one part each month. Until it’s all invested, the rest waits in cash.
This is different from investing part of your pay every month. If you don’t have the money yet, investing it as it arrives is simply investing. The question here is what to do with money you already have.
Two ways to invest £12,000 you already have
Lump sum
- All £12,000 invested on day one
- Nothing waits in cash
- Feels worst if the market falls next week
Pound-cost averaging
- £4,000 a month for three months
- The rest waits in cash meanwhile
- Later parts buy cheaper if prices fall
What Vanguard found
Vanguard compared the two over rolling one-year periods from 1976 to 2022, in markets including the UK, the US, Europe, Canada, Australia and emerging markets. The drip-feed version split the money into three parts invested a month apart1.
Investing the lump sum came out ahead between 61.6% and 73.7% of the time, depending on the market: about two-thirds overall. The longer the drip-feed period, the more often the lump sum won1.
How often the lump sum came out ahead (Vanguard, 1976 to 2022)
Across all the markets tested, about two-thirds of the time. Source: Vanguard research quoted in this lesson.
For a portfolio of all shares, the typical (median) advantage of the lump sum was 2.2%. It was 1.8% for 60% shares and 40% bonds, and 1.2% for 40% shares and 60% bonds1.
Typical (median) lump-sum advantage, by mix
The more bonds in the mix, the smaller the advantage, because bonds usually grow more slowly than shares.
Why the lump sum usually wins
Over most periods, markets have risen more often than they’ve fallen. Money waiting in cash misses out on that growth. Drip-feeding is like choosing to hold more cash for a few months, and cash has usually earned less than shares.
Where the £12,000 is in a rising market
| Lump sum | Drip-feed | |
|---|---|---|
| 1 March | £12,000 invested | £4,000 invested, £8,000 in cash |
| 1 April | £12,000 invested | £8,000 invested, £4,000 in cash |
| 1 May | £12,000 invested | £12,000 invested |
If prices rise from March to May, the money waiting in cash misses that growth. That’s why the lump sum usually wins.
The catch: when drip-feeding helps
Roughly a third of the time, drip-feeding did better, usually when markets fell soon after the start. In the worst 5% of periods for an all-share portfolio, drip-feeding was ahead by 3.6%1.
There’s also the human side. A big loss straight after investing a large sum is painful, and some people would rather not invest at all than risk it. For them, a short drip-feed can be worth the small expected cost. Vanguard suggests keeping it short, such as three months1.
The typical case and the bad case (all-share portfolio)
Drip-feeding rarely wins by much, but when it wins, it’s usually because the market fell soon after the start.
Rules for investing a lump sum
Entry
- Keep emergency savings in cash first, and only invest money you won’t need for at least five years.
- Choose a diversified fund that suits how long you’re investing for.
- If you’re comfortable, invest the sum in one go. If a sudden fall would make you panic, split it into equal monthly parts over about three months.
Exit
- Decide in advance when you’d sell, for example when you reach your goal, not because of a bad month.
Risk
- If you drip-feed, set the dates in advance and stick to them. Don’t wait for a “better” moment.
- Use a tax-free account if you can, but check its yearly limit. In the UK, an ISA has a yearly allowance.
- Remember the worst case: a lump sum invested just before a crash can be down sharply for a while.
Worked example: £12,000 to invest
- Lump sum: you invest all £12,000 in a global fund on 1 March.
- Drip-feed: you invest £4,000 on 1 March, £4,000 on 1 April and £4,000 on 1 May. Until then, the rest waits in cash.
- If the market rises over those months, the lump sum does better, because more money was invested sooner. If it falls, the drip-feed does better, because later parts buy at lower prices. History favoured the first outcome about two times in three.
Lump sum or drip-feed: pros and cons
Strengths
- Lump sum: more often ahead, because money is invested sooner.
- Lump sum: simple, with one decision instead of several.
- Drip-feed: softens the blow if markets fall straight after, and can make it easier to start.
Weaknesses
- Lump sum: a sharp fall soon after investing can be hard to sit through.
- Drip-feed: usually ends slightly behind, because cash waits on the sidelines.
- Drip-feed: tempting to delay the next part, which turns a plan into market timing.
Key terms
- Lump sum
- Investing a whole amount in one go.
- Pound-cost averaging
- Investing a fixed amount at regular intervals instead of all at once. Called dollar-cost averaging in the US.
- Rolling period
- A test repeated over many overlapping windows, for example every one-year period starting each month.
- Median
- The middle result when all results are lined up in order.
- Loss aversion
- Feeling a loss more strongly than a gain of the same size.
Sources
Numbers in the lesson, like 1, point to these sources.
Lesson complete
You have reached the end of the lesson. Now test what you learned with the five-level quiz.
Quiz zone
Test yourself: Lump sum versus drip-feeding (pound-cost averaging) quiz
Five levels, from the basics to expert judgment. Clear each level to unlock the next.
- Level 1: Foundations. Recognise the strategy and its vocabulary.
- Level 2: Mechanics. Know how the signals and rules work, and why.
- Level 3: Application. Apply the rules to realistic chart situations.
- Level 4: Numbers & risk. Size, measure and manage the trade with real calculations.
- Level 5: Mastery. Judge edge cases, failure modes and market conditions.
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The questions only. Answers and explanations appear when you take the quiz above.
Level 1: Know the basics
What does pound-cost averaging mean?
- Only buying when prices fall
- Investing a fixed amount at regular intervals
- Investing everything on day one
- Keeping all your money in cash
In the US, pound-cost averaging is called…
- lump-sum investing
- dollar-cost averaging
- index investing
- day trading
True or false: investing part of your pay each month, as you earn it, is the same choice as drip-feeding a lump sum you already have.
True or false?
In Vanguard’s research, which approach came out ahead more often?
- Keeping everything in cash
- Investing the lump sum straight away
- Drip-feeding over three months
- They were exactly equal
Level 2: Understand how it works
Why did the lump sum usually win?
- Lump sums get lower fees
- Markets always fall in the first month
- Markets rose more often than they fell, so money waiting in cash missed out
- Drip-feeding is taxed more
When did drip-feeding tend to do better?
- Never
- When markets rose steadily
- Always in January
- When markets fell soon after the start
True or false: the longer the drip-feed period, the more often the lump sum came out ahead.
True or false?
How long a drip-feed does Vanguard suggest for investors who prefer one?
- Ten years
- Five years
- Short, such as three months
- Until the market falls
In Vanguard’s test, how was the drip-feed done?
- One part a week for five years
- Twelve parts over a year
- Only when prices fell
- Three parts, invested a month apart
Level 3: Use it
You inherit £20,000 you won’t need for 15 years, and a sudden fall wouldn’t bother you. What does the research favour?
- Drip-feeding it over five years
- Keeping it all in cash
- Waiting for a crash
- Investing it as a lump sum in a diversified fund
Your friend would lie awake if £30,000 fell 20% the week after investing. What’s a reasonable approach?
- Wait until the news is good
- Invest it all in one share
- Drip-feed it in over about three months, on fixed dates
- Never invest
True or false: if you drip-feed, it’s a good idea to skip a month when the news looks bad.
True or false?
What should you do before investing any lump sum?
- Pick one share
- Keep emergency savings in cash
- Wait for the perfect moment
- Borrow more to invest
You want to put £30,000 into a UK ISA in one go. What should you check?
- Whether drip-feeding is banned
- The ISA’s yearly allowance
- Nothing: there’s no limit
- The weather
When do the rules suggest you decide when to sell?
- In advance, for example when you reach your goal
- After a bad month
- When a friend sells
- Never
Level 4: Work out the numbers
You drip-feed £12,000 in three equal monthly parts. How much is each part, in pounds?
Type a number (a month).
You drip-feed £30,000 over three months. How much do you invest each month, in pounds?
Type a number (a month).
The typical lump-sum advantage for an all-share portfolio was 2.2%. On £10,000, how much is that, in pounds?
Type a number.
In the worst 5% of periods, drip-feeding was ahead by 3.6%. On £10,000, how much is that, in pounds?
Type a number.
For 40% shares and 60% bonds, the typical lump-sum advantage was 1.2%. On £50,000, how much is that, in pounds?
Type a number.
Vanguard found the lump sum won between 61.6% and 73.7% of the time. What is the gap between those two figures, in percentage points?
Type a number (points).
If the lump sum wins about two-thirds of the time, roughly how often does drip-feeding win, in percent? Round to the nearest whole number.
Type a number (%).
Level 5: Judge the evidence
Vanguard’s result was about two-thirds in favour of the lump sum. What does that mean for your own decision?
- The lump sum has better odds, but it will still lose about a third of the time
- The result is meaningless
- Drip-feeding never makes sense
- The lump sum always wins
Why did the lump-sum advantage shrink for portfolios with more bonds?
- Bonds are always better
- It didn’t shrink
- Bonds usually grow more slowly than shares, so waiting in cash costs less
- Bonds can’t be bought as a lump sum
True or false: because the study used data from 1976 to 2022, its result is guaranteed to hold in the future.
True or false?
Someone has kept £50,000 in cash for two years because they’re afraid to invest it all at once. What does the research suggest?
- A short, fixed drip-feed is likely better than staying in cash for ever
- Keep waiting for a crash
- Invest it all in one share
- Cash is always best
What is loss aversion?
- Never losing money
- A tax rule
- A type of fund
- Feeling a loss more strongly than a gain of the same size
What is the worst case for a lump sum?
- Investing just before a crash, and being down sharply for a while
- Missing a small rise
- Paying a small fee
- Nothing can go wrong
What does median mean in “the median advantage was 2.2%”?
- The middle result when all results are lined up in order
- The biggest result
- The total of all results
- The smallest result
Which is the best one-line summary of the research?
- Always wait for a crash
- A lump sum usually wins, but a short drip-feed is a fair choice if a sudden fall would make you panic
- It makes no difference
- Always drip-feed