TL;DRThe gap fill strategy trades the statistical tendency of futures prices to return to the prior session's close after an overnight gap. Common gaps (small, no catalyst) fill most of the time. Breakaway gaps (large, catalyst-driven) often don't. The strategy enters against the gap direction after RTH opens and targets the prior close as the fill level.
A gap occurs when a session's opening price is significantly different from the prior session's close. The most common gap is between the RTH close and the next RTH open. If ES closed at 5,200 during RTH yesterday and opens at 5,212 today, there's a 12-point gap up.
But gaps also occur between other sessions. The London open can gap from the Asia close. The RTH open can gap from the London close. Any time there's a price discontinuity between one defined session and the next, a gap exists.
The gap fill strategy bets that price will return to the prior session's close (fill the gap) during the current session. This works because gaps represent a price level where no trading occurred during the reference session. The market tends to revisit these untraded levels, especially when the gap is caused by routine order flow rather than a major catalyst.
Research on ES suggests that RTH gaps of 5-15 points fill approximately 60-70% of the time within the session. Smaller gaps fill more often. Larger gaps (20+ points) fill less often, particularly when driven by a catalyst like economic data or a Fed decision.
Measure the gap. Calculate the difference between the current session's open and the prior session's close. This is your gap size. Note the direction (gap up or gap down). For RTH gaps, this is RTH close to RTH open. For London gaps, compare to the Asia session close.
Classify the gap. Is it a common gap (small, 5-15 points on ES, no clear catalyst) or a breakaway gap (large, 20+ points, driven by news, data, or a major event)? Common gaps are your setups. Breakaway gaps are not.
Wait for a failed continuation. Don't fade the gap immediately. Let the first 15-30 minutes of the session play out. If a gap-up stalls and starts to reverse, or if the opening range breakout fails in the gap direction, the fill setup is developing.
Entry. Enter in the gap-fill direction when price shows a reversal pattern after failing to extend the gap. For a gap up, this means selling after a failed breakout above the opening range high or after a break below the opening range low.
Stop loss. Place your stop above the session high (for fading a gap up) or below the session low (for fading a gap down). This gives the trade room but caps your risk at the gap extreme.
Target. The prior session's close is your primary target. This is the gap fill level. Partial profits at 50% of the gap are a common risk management approach.
Common gaps fill most of the time. These are gaps caused by routine overnight order flow, minor overseas developments, or normal pre-market activity. They're typically 5-15 points on ES. The market opens, tests the gap direction briefly, and then reverses to fill.
Breakaway gaps are dangerous to fade. These are large gaps (20+ points on ES) driven by a clear catalyst: CPI surprise, FOMC decision, major earnings, geopolitical event. The catalyst has shifted the market's view of fair value, and the gap represents a genuine repricing. Fading these is fighting the new reality.
Exhaustion gaps occur at the end of extended trends. The market gaps in the trend direction one more time, but the move is exhausted. These fill quickly and can signal a trend reversal. They're harder to identify in real time.
The key rule: if you can't identify why the gap happened, it's probably a common gap and likely to fill. If there's an obvious catalyst, be cautious about fading it.
Gap fills work best on quiet days with small gaps and no major data releases scheduled. The overnight session produced a small directional move, but there's no catalyst to sustain it during RTH. Price drifts back to the prior close as the institutional session normalizes.
Gap fills work well when the gap takes price to a known resistance or support level. If ES gaps up into yesterday's high (a natural resistance level), the combination of gap fill tendency and resistance creates a higher-probability short.
Gap fills fail when there's a genuine catalyst behind the gap. If CPI came in hot and ES gapped down 25 points, fading that gap means you're betting the inflation data doesn't matter. It usually does.
Gap fills also fail on trend days. If the gap direction is the trend direction and the opening range breaks in that direction, the gap may not only not fill but price may continue aggressively away from the prior close.
ES closed at 5,200 yesterday. Overnight, ES drifted up on light volume with no clear catalyst. ES opens at 5,209 at 8:30 AM CT, a 9-point gap up. No major economic data today.
The opening range (8:30-8:45 AM) is 5,207-5,213. At 8:50 AM, ES pushes to 5,214 (just above the OR high) but the breakout fails. A 5-minute candle closes back inside the range at 5,210. Volume on the failed breakout is below average.
Entry: short at 5,209 (below OR midpoint, after the failed breakout). Stop: 5,215 (above session high, 6 points risk, $300 per contract). Target: 5,200 (prior close / gap fill, 9 points, $450). Risk-reward: 1:1.5.
ES sells off from 5,209 and fills the gap at 5,200 by 10:30 AM. The fill took about 2 hours. Partial profit at 5,204 (half the gap) secured some gains in case the fill was incomplete.
This setup worked because: the gap was small (9 points), there was no catalyst, the opening range breakout in the gap direction failed, and volume was light.
Fading every gap regardless of size and catalyst
Only fade common gaps (small, no catalyst). Breakaway gaps driven by economic data, Fed decisions, or major news are genuine repricings. Fading them puts you on the wrong side of a fundamental shift.
Entering the fade at the RTH open before seeing how the market trades
Wait for the first 15-30 minutes. If the gap extends with volume, it's a breakaway gap and fading it is wrong. Let the opening range form and look for failed continuation before entering.
Holding for the full gap fill when momentum is turning
Take partial profits at 50% of the gap. Some gaps fill 80% and then reverse. Waiting for the exact prior close while giving back profits is unnecessary. Partial fills are wins.