🎯 In 30 seconds: If you have a lump of money ready to invest for the long run, putting it all in at once has historically come out ahead about two-thirds of the time. Spreading it out (dollar-cost averaging) wins the other third and feels better if prices drop right after you start. Either is far better than leaving the money in cash because you can’t decide.
Two different situations
Investing from each paycheck is automatic dollar-cost averaging. You invest money as you earn it. There is no lump-sum choice here, and it works well.
Investing a lump you already have (an inheritance, a bonus, a home sale, a rollover sitting in cash) is where the question comes up. You can buy now, or spread the purchases over months.
What Vanguard’s research found
Vanguard researchers Megan Finlay and Josef Zorn published “Cost averaging: Invest now or temporarily hold your cash?” in February 2023. They compared investing at once with splitting the money into three monthly pieces, across rolling one-year periods from 1976 to 2022.
| How often lump sum came out ahead | Between 61.6% and 73.7% of the time, depending on market |
| Median edge, 100% stocks | 2.2% higher after one year |
| Median edge, 60/40 stocks and bonds | 1.8% higher |
| Median edge, 40/60 | 1.2% higher |
The reason is simple. Markets have risen more often than they have fallen, so money waiting in cash usually misses some gains. Vanguard also found the longer you take to invest, the more often lump sum wins.
The flip side: lump sum had a wider range of outcomes. When it went badly, it went worse than averaging in. That is why Vanguard notes that cost averaging may suit risk-averse investors, if it keeps them from abandoning the plan.
Worked example
Sam has $60,000. Option A buys all at once at $100 a share: 600 shares. Option B buys $10,000 a month for six months. Two made-up price paths show the trade-off:
| Path | Monthly prices | Lump sum value at the end | Averaging value at the end |
|---|---|---|---|
| Dip, then recover | $100, 90, 80, 90, 100, 110 | 600 × $110 = $66,000 | 638.13 shares × $110 = $70,194 |
| Steady rise | $100, 105, 110, 115, 120, 125 | 600 × $125 = $75,000 | 536.44 shares × $125 = $67,055 |
Averaging wins when prices fall early, because the same $10,000 buys more shares at low prices. Lump sum wins when prices climb, which history says is the more common path.
How people commonly decide
- Check the date. Money needed within a few years does not belong in stocks either way. See where short-term money goes.
- Choose the mix first. Many people who feel nervous about a lump sum are really holding a mix that is too aggressive for them. A more conservative mix, invested at once, can be the better fix.
- If you average in, set a short fixed schedule (for example 3 to 6 months) and automate it. Write the dates down.
- Do not make it conditional on headlines, like “I’ll invest after the market drops.” That turns a plan into market timing.
- Park the waiting money somewhere that pays interest, such as a money market fund or T-bills.