What This DCA Calculator Shows
Most monthly investors pick a calendar date for convenience, often the 1st because it lines up with payday. This tool compares that default to the Accumulator across roughly twenty years of SPY and QQQ history. Calendar day alone produces a small drift: later contribution days finish slightly behind earlier ones. Adding the Accumulator’s systematic sizing, with capital reserved for discount windows, opens a measurable Alpha Gap versus blind payday DCA.
Timing Alone vs. Timing Plus Systematic Sizing
Step 1 lets you scrub each calendar day and compare plain DCA terminal wealth to day-1 blind DCA across days 1–28. Outcomes trend slightly lower later in the month. That is a small calendar effect, not a random scatter. Step 2 keeps the same day control but applies systematic sizing. Day 20 separates from the pack, not because of a calendar superstition, but because that schedule interacts with how the Accumulator holds and deploys capital across the month.
How to Read the Alpha Gap
The Alpha Gap is the terminal wealth difference between the Accumulator path and blind first-of-month DCA over the same contribution schedule. The underlying research is fixed at $1,000 per month. The calculator scales that published delta to your selected monthly amount for illustration.
- Does the day of the month you invest actually matter?
- Across 20 years of SPY and QQQ data, plain monthly DCA finishes a bit lower as you invest later in the month. That is a small calendar effect on its own. Timing plus systematic sizing opens a much larger Alpha Gap.
- What is the Payday Trap?
- The Payday Trap is blind monthly investing on fixed early-month dates, often when retirement inflows create a temporary price floor. The Accumulator waits and sizes contributions based on systematic posture instead of a fixed calendar amount.
- How is the Alpha Gap calculated?
- The Alpha Gap is the terminal wealth difference between the Accumulator system and blind payday DCA over the same backtest window. The calculator scales that published $1,000/month result to your selected monthly contribution.
- Is this investment advice?
- No. Breadth Signal publishes quantitative research for education. Past backtested results do not guarantee future performance. See our Terms of Service.
- What is a War Chest?
- The War Chest is cash held in reserve so the Accumulator can invest more when a strong opportunity appears, instead of missing it for lack of available money.
- How current is this data?
- This calculator uses backtested SPY and QQQ data through 2026-08-21, refreshed periodically. Figures may shift slightly as more recent market data is included.
- Why do days 27 and 28 look worse in the timing comparison?
- Some shorter months don't have a trading session that late in the calendar. Contributing on day 27 or 28 means those months get skipped entirely, so less money ends up invested overall. That's a real cost of picking a very late date, not an error in the data.
- Does the Alpha Gap scale exactly with my monthly amount?
- The underlying backtest is run at $1,000 a month. The calculator scales that result in proportion to whatever amount you choose. This is a close approximation, not a separate backtest at every dollar amount, and it's stated for transparency rather than precision at every possible contribution level.
- Why does the Accumulator's reserve earn a different return than blind DCA's reserve cash in this comparison?
- Blind DCA's reserve is modeled at a standard savings yield, the way most people actually treat uninvested cash. The Accumulator's War Chest is modeled earning historical T-bill rates instead. Both reflect realistic behavior. Part of the gap comes from timing and sizing, and part comes from this difference in how reserve cash is treated.