ArthaPilot Research
Lump sum vs. dollar-cost averaging
What U.S. market history shows when the full investment is available on day one.
By ArthaPilot Research
Published 2026-07-28
Updated 2026-09-05
Data through July 2026
Suppose an investor has $100,000 ready to invest. One approach buys the market at once. The other divides the principal into 12 equal portions for monthly purchases, with the first purchase made immediately. Each later portion is invested with the interest it earned while waiting. We ran both approaches from every eligible month-end in the extended U.S. large-cap record and used the same 10-year end date for each pair.
Immediate investment ended ahead in 68.2% of 1,081 periods. The average annualized difference was +0.29 percentage points. The median ending-wealth difference was +$9,234 (immediate investment minus DCA). DCA led in 31.8% of periods.
Both strategies started with the same capital and bought the same market series. Waiting cash earned the historical Treasury-bill return. Results are nominal. Adjacent start dates share most of their market history, so the periods are observations from one record rather than independent trials.
What the record shows
Time in the market won more often
Investing immediately put all available cash to work on the start date. DCA left part of it waiting throughout the deployment period. In a record with more rising than falling deployment windows, that delay usually cost some return. The outcome went the other way when prices fell soon after the start and later purchases bought more shares.
The 68.2% figure describes these rolling historical periods. It is not a probability for the next investor. The sample contains one realized U.S. market history, and overlapping periods are closely related.
Most gaps were modest
The median ending-wealth gap was +$9,234 on an initial $100,000. Many starting months finished near the center of the distribution, even when one approach ended ahead. The tails show that the start date still mattered: annualized gaps ranged from −6.60 percentage points to +5.32 percentage points.
Immediate-investment wins averaged 0.90 percentage points a year. DCA wins averaged 1.03 percentage points. Win frequency tells us which approach finished ahead more often; those margins show how much the winning periods separated.
Figure 01
The size and frequency of the return gap
Negative favors DCA and positive favors immediate investment, in half-point bins.
Period counts by gap size
Source: ArthaPilot historical calculation. SPY.SIM; 10-year overlapping periods. Nominal returns.
The first 12 months set the result
The holdings differed only while DCA was still deploying cash. Once the final purchase was made, both approaches held the same asset. The share count accumulated during those first months carried through to the common end date.
When the market fell during deployment, DCA finished ahead in 90.0% of periods. When it rose, immediate investment finished ahead in 88.4%. Rising windows accounted for 74.2% of the sample.
Figure 02
Market moves while cash was being deployed
Values by deployment direction
Source: ArthaPilot historical calculation. SPY.SIM; 10-year overlapping periods. Nominal returns.
The result under other assumptions
Two choices have a direct effect on the comparison: how long DCA takes and what the uninvested balance earns. The comparisons below change one choice at a time while keeping the market series, starting dates, capital, and 10-year horizon fixed.
Longer schedules widened the cost of waiting
Immediate investment led in 61.1% of periods against a 3-month schedule, with a median ending-wealth advantage of $2,227. At 24 months, the win rate was 71.6% and the median advantage reached $18,317. Leaving more cash undeployed for longer made the rising-market periods more expensive.
Figure 03
Changing the purchase schedule
Exact values by schedule
Source: ArthaPilot historical calculation. SPY.SIM; 10-year overlapping periods. Nominal returns.
Interest on waiting cash narrowed the gap
Crediting the waiting balance with historical Treasury-bill returns lowered the immediate-investment win rate to 68.2%, from 72.8% when cash earned nothing. Interest compensated for part of the delay, though immediate investment still led more often in both cases.
What prior research found
The direction of this result is well established. Vanguard found immediate investment ahead in 68% of its global equity observations. Its comparison used a three-month schedule, a one-year horizon, and no return on waiting cash. PWL used the closest design to ours: a 12-month schedule, Treasury-bill returns on waiting cash, and rolling 10-year periods. Immediate investment led in 70.59% of its U.S. observations.
- Vanguard, 2023. Cost averaging: invest now or temporarily hold your cash?
- PWL Capital, 2020. Dollar cost averaging vs. Lump sum investing.
External studies provide context only; no third-party result enters the ArthaPilot calculation.
Four periods in the record
Four fixed rules chose the periods below: the widest immediate-investment advantage, the result closest to the average immediate win, the most recent immediate win, and the widest DCA advantage. The last row keeps a period where waiting paid off in view alongside the immediate-investment wins.
The widest immediate-investment advantage began in March 1933. The market gained 90.3% during the deployment period, and immediate investment finished $126,007 higher at the end of the horizon. The typical case began in February 1979 and ended with a gap of $34,906.
The most recent immediate-investment win began in July 2016. The DCA counterexample began in August 1931. The market lost 53.7% during deployment. DCA finished $106,660 higher in that period.
Conclusion
For cash available on day one, immediate investment had the higher historical win rate in the base case and every deployment-length variant shown above. Its edge grew as the purchase schedule lengthened and as the return on waiting cash fell.
DCA reduced exposure to a decline immediately after the start date. That benefit appears clearly in the falling deployment windows. An investor may value that protection from near-term drawdown or regret, even when the historical return record favored entering sooner.
This study covers lump sums already available at the start. It does not cover periodic income invested as it is earned, multi-asset portfolios, taxes, trading costs, or plans that change after a loss.
Methods and limitations
The market series is SPY.SIM, covering July 1926 through July 2026. Returns use extended U.S. large-cap total return data at monthly frequency. See the .SIM methodology for how the extended history is constructed.
First DCA installment is invested immediately; remaining equal installments are invested at successive month-end observations. Both approaches begin with the same capital, buy the same market series, and use one terminal date. Results are nominal and denominated in USD. Rolling windows overlap and are not statistically independent.
- The equity path uses ArthaPilot's extended U.S. large-cap total-return series, including reconstructed history before SPY began trading.
- Monthly observations use the final available trading-day value in each calendar month. Missing months are not filled, and incomplete windows are excluded.
- The historical sample is capped at July 2026 so the published result and interactive comparisons remain reproducible as new market data arrives.
- Results are nominal and are not adjusted for inflation, taxes, fees, bid-ask spreads, or implementation slippage.
Archived edition: July 2026. Inputs were captured on 2026-09-05 from the canonical extended-history construction, using Yahoo Finance for the live SPY segment. The history ends July 31, 2026; source revisions available on the capture date are included. This is a reproducible archive, not a point-in-time record of what was known at each historical start.
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