Lump Sum vs Dollar-Cost Averaging
Got a windfall? Markets rise more often than they fall, so investing it all at once usually wins. Here’s the backtest across every starting point since 1928.
| Data | Series | Provider |
|---|---|---|
| S&P 500 annual total returns | 1928 to 2025 | NYU Stern / Damodaran |
| Lump sum vs DCA study | Rolling 12-month comparisons | Vanguard |
Lump sum invests the whole amount at the start of year one; DCA invests an equal slice at the start of each year over the spread, with uninvested cash earning nothing, and both are valued at the end of the spread. Because stocks rise in about two-thirds of years, lump sum usually wins; dollar-cost averaging mainly helps when you would have bought right before a crash, and its real value is behavioral. The Vanguard study finds lump sum wins about 68% of rolling 12-month periods, and spreading over more years widens that edge.
About this tool
A windfall arrives: invest it all today, or average in over months? This tool answers with history rather than opinion, backtesting both approaches across every starting year since 1928 to show how often the lump sum won, by how much, and when averaging in actually helped.
The historical verdict is lopsided: because markets rise in most years, the lump sum has beaten dollar-cost averaging roughly two times out of three. Averaging in is better understood as regret insurance, a fair price to pay if a big immediate loss would push you to abandon the plan entirely.
How often does lump sum beat dollar-cost averaging?
In roughly two-thirds of historical 12-month windows since 1928. Cash waiting to be deployed missed more gains than it dodged losses, most of the time.
When did averaging in win?
In the windows that led into major bear markets: 1929, 2000, 2008. DCA wins precisely when stocks fall shortly after the windfall arrives, which is unknowable in advance.
What about investing at an all-time high?
All-time highs are the market's normal state in a rising series, and returns following highs have historically been unremarkable compared with any other starting point. Waiting for a dip has been the more expensive habit.