Futures Gaps: When They Fill vs. When They Extend — and the Statistics That Tell You Which

The Gap Fill Myth That Costs Retail Traders Money

The most repeated piece of market wisdom that novice futures traders absorb is "gaps always fill." It sounds logical — what goes up must come down, and an open gap is an inefficiency the market will correct. The reality: gaps do fill at a higher rate than random chance would predict, but "always fill" is simply false. Applying this rule indiscriminately produces a trading strategy that loses money on the significant minority of gaps that extend into full trend days.

The professional approach to gaps is probabilistic and conditional: some gap types have 75%+ fill rates in ES and NQ data; other gap types have sub-40% fill rates and are better traded as momentum extensions. Knowing which type you are facing before the open determines your entire session strategy.

Defining Gaps in ES and NQ Futures

In equity futures, a gap is the difference between the previous session's close (4:15 PM ET) and the current session's open (9:30 AM ET). The size of the gap is measured in points:

• Small gap: 0–5 ES points (0–0.1% of index value)
• Medium gap: 5–15 ES points (0.1–0.3%)
• Large gap: 15–30 ES points (0.3–0.6%)
• Extreme gap: 30+ ES points (0.6%+)

Gap direction matters equally: gap-up opens above the prior close; gap-down opens below. The statistics for fills differ significantly by direction in certain market regimes.

Important distinction: the gap is measured from the prior regular-hours close (4:15 PM), not from the Globex overnight session price. The overnight session price at 9:29 AM is not the gap reference — the 4:15 PM close is.

Statistical Gap Fill Rates by Gap Type

Historical ES futures data (multiple-year samples across various market regimes) produces the following fill rate estimates by gap category:

Small gaps (0–5 points): ~80–85% fill rate. Small gaps represent overnight noise — minor position adjustments, low-conviction pre-market movement. The regular-hours session almost always absorbs small gaps within the first 30–60 minutes. These are the highest-probability fill setups and are best traded as fades: if the market gaps up 3 points, fade the gap (sell) early in the session with a stop above the opening print.

Medium gaps (5–15 points): ~60–70% fill rate. Medium gaps require more context analysis before deciding fill vs. extend. Catalyst-driven gaps in this range (pre-market news, earnings from major index components, FOMC-related positioning) have lower fill rates than structural gaps without clear catalyst. Apply the filter criteria below before trading these as fills.

Large gaps (15–30 points): ~40–55% fill rate. Large gaps are approximately coin-flip probability. This range is where the fill vs. extend analysis is most critical. Large gaps that occur on high-conviction catalysts (FOMC rate decisions, major economic data surprises) have lower fill rates; large gaps that occur on thin pre-market volume without clear catalyst have higher fill rates.

Extreme gaps (30+ points): ~25–35% fill rate. The "gaps always fill" rule fails most dramatically here. When ES opens 50+ points below the prior close on a risk-off event, fading the gap immediately at the open is statistically unfavorable. These gaps extend with trend for the full session more often than they fill. The correct trade is the opposite of the fill: participate in the direction of the gap with the trend.

The Four-Factor Gap Classification System

Before each session, apply this four-factor analysis to classify the gap as high-probability fill, low-probability fill, or neutral:

Factor 1: Catalyst quality. Is there a clear fundamental catalyst for the gap? FOMC decision, CPI print above/below expectations, major index component earnings — these catalysts justify repricing and reduce fill probability. No clear catalyst (gap formed during thin overnight session on low volume) — higher fill probability.

Factor 2: Overnight volume. Low overnight Globex volume on the gap move suggests institutional absence — the gap was formed by algorithmic thin-market noise rather than genuine positioning. High overnight volume on the gap move suggests institutional commitment to the new price level — lower fill probability.

Factor 3: Market regime. In trending bull markets, gap-up fills are less common because the trend direction supports the gap direction. Buying is systematic; the gap simply reflects daily trend continuation. In bear markets or consolidation regimes, gaps against the primary trend are more likely to fill (buyers/sellers defending the trend direction from the prior direction).

Factor 4: Gap size relative to ATR. A gap that represents less than 0.5× the daily ATR is within normal volatility range — high fill probability. A gap that represents 1.5–2× the daily ATR is a significant statistical outlier — lower fill probability, higher extension probability.

Scoring: 3 or 4 factors pointing toward fill = high-probability fill setup. 2 factors each way = neutral, trade OR breakout instead. 3 or 4 factors pointing toward extension = fade the fade, trade with the gap direction.

How to Trade High-Probability Gap Fills

When the four-factor analysis identifies a high-probability fill, the trade structure:

• Wait for the opening 15 minutes before entering. The first 15 minutes reveal whether the fill attempt has conviction — is volume expanding as price moves toward the gap fill level, or is volume thin on the initial move?
• Entry: first pullback in the fill direction. Do not enter at the open. Wait for the initial opening move to establish direction, then enter on the first retracement in the fill direction. If ES gaps up and begins filling (moving down toward the prior close), wait for the first bounce attempt that fails, then enter short as the bounce fails.
• Target: prior session close (the gap fill level). This is the mechanical target. Do not get greedy beyond the gap fill on fill trades — the trade thesis completes at the fill.
• Stop: above the opening print (for gap-down fills) or below the opening print (for gap-up fills). If the opening print is defended and price moves back to the gap open before filling, the fill thesis is invalidated.

How to Trade Gap Extensions (When Gaps Don't Fill)

When the four-factor analysis identifies a low-probability fill (extension likely), the trade structure reverses:

• Direction: trade with the gap, not against it
• Entry: opening range breakout in the gap direction — after the OR establishes (9:30–10:00 AM), enter on a close above the OR high (for gap-up) or below the OR low (for gap-down)
• Target: measured move equal to the gap size from the opening print, or the next KPL level in the gap direction
• Stop: below the OR low (for gap-up extensions) or above the OR high (for gap-down extensions)

The psychological challenge of extension trades: when ES gaps down 25 points, every retail intuition says "this is overdone, it must bounce." The statistical reality says the opposite on extreme gaps. Overriding this intuition requires pre-session analysis that commits to the extension approach before the open, while you are still objective.

Partial Fills: The Most Common Outcome

Many gaps result in partial fills — price moves toward the prior close but stops short (fills 50–70% of the gap) and then reverses. Partial fills are common on medium gaps with mixed factor scores. The partial fill pattern reveals both sides of the market: buyers/sellers defending the gap level (preventing full extension) and opposing traders defending the prior close (preventing full fill).

For partial fill management: set a secondary target at 50% of the gap distance as a scale-out point. Take half the position off at the 50% fill level and let the rest run to the full fill target. This captures the most reliable portion of the fill move without requiring the full fill to generate a profitable trade.

Building a Pre-Session Gap Analysis Routine

The gap analysis workflow runs each morning before 9:30 AM as part of the daily trade plan:

1. Calculate gap size and direction versus prior 4:15 PM close
2. Check for overnight catalysts (FOMC, CPI, earnings from major components)
3. Review overnight Globex volume — was the gap formed on volume or on thin overnight trading?
4. Check current market regime (daily chart trend direction)
5. Compare gap size to 14-period daily ATR
6. Score the four factors and classify: high-probability fill, neutral, or high-probability extension
7. Mark the prior session close (gap fill target) on the chart
8. Mark the current session opening print (extension stop reference) on the chart

This analysis takes 3–5 minutes and pre-defines your opening bias before the market opens. The YMI daily KPL deliverable includes gap analysis and opening bias classification each morning — removing the need to build this workflow independently.

Stop trading every gap as a fill and start trading the ones with statistical backing. YMI Intro Trader includes the daily gap and KPL analysis that gives systematic traders a pre-session roadmap every morning of the trading week.