Dollar-cost averaging vs lump-sum investing has a clear answer in the historical record: investing everything at once wins about two-thirds of the time. Vanguard's February 2023 study found that a lump sum beat cost averaging in 68% of one-year periods across global markets, and that both approaches beat staying in cash roughly 70% of the time [1]. The 2026 market repeated the pattern. An investor who put $120,000 into the S&P 500 (SPX) on December 31, 2025 held about $131,600 on July 21, 2026, while an investor who spread the same amount over seven monthly installments held about $128,900 including interest on the idle cash, even though the averaging plan bought some shares during the March drawdown [2] [3].
Dollar-cost averaging vs lump-sum investing: what the evidence shows
Vanguard researchers Megan Finlay and Josef Zorn compared the two strategies across the United States, the United Kingdom, Australia, Canada and the euro area, using historical data and simulated return paths [1]. Their headline result: a lump sum outperformed cost averaging roughly two-thirds of the time, 68% in the global market illustration, when wealth was compared after one year [1]. The reason is simple. Between 1976 and 2022, U.S. stocks beat 3-month Treasury bills in 76% of periods and U.S. bonds beat bills in 68% [1]. Money waiting in cash forgoes that risk premium, and cost averaging is, by construction, a plan to hold cash for a while.
The study is careful to add that cost averaging is not a mistake relative to doing nothing. Cost averaging beat remaining in cash 69% of the time [1]. The ranking is therefore: lump sum first, cost averaging second, cash last, in most historical periods.
When averaging wins
Cost averaging wins when prices fall during the averaging window. The Vanguard paper shows that the lump sum outperforms in all but the worst outcomes; in the lowest percentiles of one-year returns, averaging leaves the investor with more wealth because it bought later at lower prices [1]. The strategy is best understood as insurance against a bad first year, paid for with a lower expected return.
A 2026 example with real prices
The first seven months of 2026 contained exactly the kind of drop that averaging is meant to soften. The S&P 500 closed 2025 at 6,845.50, drifted to 6,878.88 at the end of February, fell to 6,528.52 on March 31, then rallied to 7,209.01 by April 30, 7,580.06 by May 29 and 7,499.36 by June 30 [2]. On July 21, 2026 the index closed at 7,509.20, up 9.7% for the year [2].
| Strategy, $120,000 total | Purchase dates | Value on July 21, 2026 |
|---|---|---|
| Lump sum | Dec 31, 2025 at 6,845.50 | $131,635 |
| Seven monthly installments of $17,143 | Dec 31 to Jun 30 month-end closes | $127,793 in shares plus about $1,088 of T-bill interest on idle cash |
Calculations use S&P 500 price closes and 3-month Treasury bill yields from FRED; dividends are excluded for both strategies [2] [3]. The averaging plan bought its cheapest installment on March 31 at 6,528.52, about 4.6% below the December 31 price, but five of its seven purchases were made above the lump-sum entry price and one at the same price. The lump sum finished ahead by roughly $2,750, or about 2.1%. Had the March drawdown extended through the summer, the ranking would have reversed; that is the trade the averaging investor accepts.
Cash was not free in 2026, but it was not enough
A common argument for averaging in 2026 is that idle cash earns a respectable yield. Three-month bills paid 3.57% at the end of 2025 and 3.74% on July 21, 2026 [3]. Over the seven-month window that produced about $1,088 of interest on the uninvested balance, which narrowed but did not close the gap. The Vanguard finding that cash is the weakest of the three choices in most periods held again [1].
Why the choice is really about behavior
Most investors do not face this decision with a large windfall. They invest from each paycheck, which is cost averaging by necessity and needs no defense. The lump-sum question applies to inheritances, bonuses, business sales and rollovers. For those cases, the evidence favors investing at once if the portfolio matches the investor's risk tolerance. If the alternative is that the investor will hold cash indefinitely out of fear, a scheduled averaging plan of three to twelve months is a reasonable second best because it gets the money invested at all [1].
- Set the target allocation first; the averaging debate is only about how fast to reach it.
- Keep the averaging window short. A one-year plan captures most of the behavioral benefit; multi-year plans mostly forfeit returns.
- Automate the installments so a rally does not tempt the investor to stop early and a decline does not tempt the investor to pause.
- Track the entry prices. Daily and monthly index history is available on DataPorium's stock market page [4].
The fair counterpoint: valuation. When forward earnings multiples are well above their long-run averages, some analysts argue the expected equity premium is thinner and the cost of waiting is lower. Vanguard's results are averages across all historical starting points, so they do not settle that debate; investors who cannot tolerate a large early loss may consider averaging as a form of regret insurance rather than a return strategy [1].
Lump-sum investing wins about two-thirds of the time, and 2026 was one of those times despite a nine percent spring drawdown.
Key takeaways
- Vanguard's 2023 study found lump-sum investing beat cost averaging 68% of the time over one year, and both beat cash about 70% of the time [1].
- In 2026, $120,000 invested in the S&P 500 on December 31, 2025 was worth about $131,600 on July 21, versus about $128,900 for seven monthly installments including cash interest [2] [3].
- Averaging bought its cheapest shares at the March 31 low of 6,528.52, but most installments were made above the lump-sum entry price [2].
- Cost averaging is insurance against a bad first year, useful for investors who would otherwise stay in cash.
Frequently asked questions
Is lump-sum investing better than dollar-cost averaging?
Historically, yes, about two-thirds of the time. Vanguard found a lump sum beat cost averaging in 68% of one-year periods across global markets, because cash waiting to be invested forgoes the equity risk premium [1].
Did dollar-cost averaging beat a lump sum in 2026?
No. Using S&P 500 closes from FRED, $120,000 invested on December 31, 2025 was worth about $131,600 on July 21, 2026, while seven monthly installments were worth about $128,900 including T-bill interest on idle cash [2] [3].
When does dollar-cost averaging win?
When prices fall during the averaging window. In the worst historical one-year outcomes, averaging left investors with more wealth than a lump sum because later purchases were made at lower prices [1].
How long should a dollar-cost averaging plan last?
Shorter is generally better. Vanguard's analysis compares wealth after one year, and longer plans hold cash longer, which lost to both stocks and bonds in most periods since 1976 [1].
