Lump sum vs. dollar-cost averaging
What U.S. market history shows when the full investment is available on day one.
Given $100,000 on day one, we compare immediate investment with splitting the principal into 12 equal portions invested monthly. The first portion is invested immediately; each later portion is invested with the interest it earned while waiting. We compare both approaches from each eligible month-end in the extended U.S. large-cap record, using the same 10-year end date.
Immediate investment ended ahead in 68.2% of 1,081 periods. Its average annualized difference was +0.29 percentage points. The median ending-wealth gap was +$9,234 (immediate investment minus DCA). DCA led in 31.8% of periods.
Both approaches use the same capital and market series. Waiting cash earned the historical Treasury-bill return. Results are nominal. Adjacent start dates share most of their history, so these observations are not independent trials.
What the record shows
Immediate investment finished ahead more often
Investing immediately put all available cash to work on the start date. DCA left some cash uninvested during deployment. In this sample, more deployment windows rose than fell, so waiting usually cost some return. When the market fell during deployment, later DCA purchases bought more shares and could offset that cost.
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.
Win frequency and gap size answer different questions
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
| Annualized gap (percentage points) | Rolling periods | Share of periods |
|---|---|---|
| -7.00 to -6.50 | 1 | 0.1% |
| -6.50 to -6.00 | 0 | 0.0% |
| -6.00 to -5.50 | 2 | 0.2% |
| -5.50 to -5.00 | 0 | 0.0% |
| -5.00 to -4.50 | 0 | 0.0% |
| -4.50 to -4.00 | 2 | 0.2% |
| -4.00 to -3.50 | 6 | 0.6% |
| -3.50 to -3.00 | 6 | 0.6% |
| -3.00 to -2.50 | 14 | 1.3% |
| -2.50 to -2.00 | 14 | 1.3% |
| -2.00 to -1.50 | 34 | 3.1% |
| -1.50 to -1.00 | 58 | 5.4% |
| -1.00 to -0.50 | 89 | 8.2% |
| -0.50 to 0.00 | 118 | 10.9% |
| 0.00 to 0.50 | 250 | 23.1% |
| 0.50 to 1.00 | 220 | 20.4% |
| 1.00 to 1.50 | 139 | 12.9% |
| 1.50 to 2.00 | 79 | 7.3% |
| 2.00 to 2.50 | 32 | 3.0% |
| 2.50 to 3.00 | 9 | 0.8% |
| 3.00 to 3.50 | 4 | 0.4% |
| 3.50 to 4.00 | 0 | 0.0% |
| 4.00 to 4.50 | 1 | 0.1% |
| 4.50 to 5.00 | 1 | 0.1% |
| 5.00 to 5.50 | 2 | 0.2% |
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
| Market fell while deploying | Market rose while deploying | |
|---|---|---|
| Share of periods | 25.8% (279) | 74.2% (802) |
| Average market move | −14.0% | +19.6% |
| Usually finished ahead | Monthly schedule, 90.0% | Invest immediately, 88.4% |
| Average annualized gap | −1.09 percentage points | +0.77 percentage points |
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
| Deployment period | Immediate investment ahead | Average annualized gap | Median ending-wealth gap |
|---|---|---|---|
| 3 months | 61.1% | +0.05 percentage points | +$2,227 |
| 6 months | 64.8% | +0.13 percentage points | +$4,014 |
| 12 months | 68.2% | +0.29 percentage points | +$9,234 |
| 18 months | 69.7% | +0.44 percentage points | +$14,319 |
| 24 months | 71.6% | +0.59 percentage points | +$18,317 |
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.
| Return on waiting cash | Immediate investment ahead | Average annualized gap | Median ending-wealth gap |
|---|---|---|---|
| Treasury-bill returns | 68.2% | +0.29 percentage points | +$9,234 |
| No return | 72.8% | +0.45 percentage points | +$13,075 |
What prior research found
Vanguard compared MSCI World returns from 1976 to 2022. With a three-month schedule, one-year horizon, and no return on waiting cash, immediate investment finished ahead in 68% of periods. Vanguard also modeled loss aversion and found that staging could be more tolerable for some highly loss-averse investors. PWL tested a 12-month schedule, credited waiting cash with Treasury-bill returns, and compared rolling 10-year periods across six developed markets. Immediate investment led in 70.59% of U.S. periods and 64.89% across markets.
- 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 rules pick 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.
| Case | Period | Market during deployment | Annualized gap | Ending-wealth gap |
|---|---|---|---|---|
| Largest immediate-investment edge | Mar 1933 to Mar 1943 | +90.3% | +5.32 percentage points | +$126,007 |
| A typical immediate-investment win | Feb 1979 to Feb 1989 | +29.3% | +0.90 percentage points | +$34,906 |
| Most recent immediate-investment win | Jul 2016 to Jul 2026 | +13.7% | +0.60 percentage points | +$20,660 |
| Largest DCA edge | Aug 1931 to Aug 1941 | −53.7% | −6.60 percentage points | −$106,660 |
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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