Direct Answer
A price gap appears on a chart whenever one bar's range doesn't overlap with the range of the bar before it, most visibly on daily charts, where an overnight or pre-market move can leave a visual void between yesterday's close and today's open. That void represents a stretch of prices where no trade actually occurred on that instrument.
Key Takeaways
- A gap fill occurs when price retraces to close a prior price gap, trading back through the full range that was skipped between two sessions or bars.
- A gap isn't "filled" the instant price touches its edge, it requires trading all the way through the skipped range, back to the level where the gap began.
- Not every gap fills. Common gaps in quiet conditions fill often; breakaway and exhaustion gaps tied to a strong trend can stay unfilled for a long time or indefinitely.
- There is no fixed timeframe for a fill, it can happen within the same session, or take days, weeks, or longer.
- A gap fill is often confused with a gap fade trade: the fill is the price event, the fade is a strategy that bets on that event happening.
Gap Fill Pattern
A gap fill occurs when price retraces to close a prior price gap, trading back through the full range that was skipped. Gaps form when a chart shows no trading between one bar's range and the next, commonly at the open after news, earnings, or a heavy order imbalance, and a fill happens when later price action revisits and trades through that entire untraded range.
What Is a Gap Fill?
A price gap appears on a chart whenever one bar's range doesn't overlap with the range of the bar before it, most visibly on daily charts, where an overnight or pre-market move can leave a visual void between yesterday's close and today's open. That void represents a stretch of prices where no trade actually occurred on that instrument. A gap fill is what happens when subsequent price action moves back into that void and trades through every level inside it, effectively erasing the gap from a "has this been retraced" standpoint.
Filling a gap is a statement about price coverage, not about direction on its own. A gap can fill because the initial move reverses outright, or because a slower, unrelated drift eventually carries price back through the range days or weeks later. Either way, the defining fact is the same: every price level inside the original gap has now traded.
How a Gap Fill Forms
The sequence starts with the gap itself: a bar whose entire range sits above or below the prior bar's range, leaving a skipped band of prices with no trading history. From there, a fill requires two things, price must reverse or drift back toward the gap, and it must trade far enough through the skipped range to reach the far edge, not just dip into it.
Traders generally track the two edges of the gap separately: the near edge (closest to where price currently is) and the far edge (the level that must be reached for the gap to count as fully filled). A move that only reaches the near edge is a partial fill; the gap isn't considered closed until price trades through to the far edge as well.
Gap Fill Example
The chart below shows a deterministic, illustrative example: a gap-down bar leaves a visible void below the prior bar's low, then subsequent bars trade back up through that void until the gap's far edge is fully retraced. Toggle between two possible continuations: a confirmation (price climbs back through the entire gap, completing the fill) and a failure/look-alike (price continues lower instead, leaving the gap unfilled).
How to Trade a Gap Fill
Classify the gap first
Not all gaps behave the same way. A common gap forming in a quiet, range-bound stretch fills far more often than a breakaway gap that launches a new trend or an exhaustion gap that marks a trend's final push. Reading the broader trend and volume context around the gap before assuming a fill is coming matters more than the gap's size alone.
Track the far edge, not just the near edge
A partial retrace into the gap is not the same as a completed fill. Traders who plan around a full fill define both edges of the gap in advance and treat the far edge, not the first touch, as the level that confirms the pattern.
Define invalidation before acting
Because there's no guarantee a gap fills at all, a fill-based trade needs a defined invalidation level, commonly the low (or high) of the bar that created the gap. If price makes a new extreme beyond that level instead of retracing, the fill thesis is invalidated and the move is behaving more like a continuation than a retrace.
Common Gap Fill Mistakes
- Assuming every gap fills, treating "gaps always fill" as a rule rather than a tendency ignores how differently breakaway and exhaustion gaps behave compared to common gaps.
- Calling a partial retrace a full fill, price touching the near edge of the gap is not the same as trading through to the far edge.
- Ignoring the trend context around the gap, a gap that forms as part of a strong, high-conviction breakout is a poor candidate for a near-term fade back to fill.
- Trading the fill without an invalidation level, entering a fill-based position without a defined stop beyond the gap bar's own extreme leaves no clear point where the thesis is wrong.
Gap Fill vs. Similar Concepts
| Term | What it emphasizes | Key difference from a gap fill |
|---|---|---|
| Gap fill | Price trading back through the full range a prior gap skipped | Baseline, a completed retrace event, not a trade or a level by itself |
| Gap fade | A trading approach that bets on a fill happening | A strategy built around the gap-fill idea, typically entered soon after the gap forms, not the price event itself |
| Gap and go | Continuation in the gap's direction instead of a retrace | The opposite outcome to a fill, price extends away from the prior close rather than back toward it |
| Liquidity sweep | Resting orders clustered beyond a support or resistance level | A different mechanism entirely, a sweep targets stop-loss liquidity at a level, while a fill is about retracing a skipped price range |
Limitations of Gap Fill Analysis
A gap fill is read from price coverage alone; it says nothing about why the gap formed or whether the same forces that produced it are still in play. It also carries no guarantee, a gap that has filled quickly in the past is not obligated to behave the same way again, and some gaps, particularly breakaway and exhaustion gaps inside a strong trend, can remain unfilled for a very long time or never fill at all. Like any single pattern, a gap fill reading works best combined with trend context, gap classification, and a defined invalidation plan rather than used in isolation.
Touching the Edge Is Not Filling the Gap
A fill requires price to trade back through the entire untraded range, from the near edge to the far one. Price reaching the near edge and turning is a partial retrace, and describing it as a fill quietly changes the record: a strategy that counts near-edge touches will report a much higher fill rate than one that measures properly, and the two will disagree about how the tendency behaves.
The bigger issue is the rule people carry into this: that gaps always fill. Common gaps in quiet conditions do fill often, which is where the impression comes from. Breakaway and exhaustion gaps tied to a real change in circumstances can stay open for a very long time or never fill, and those are precisely the gaps most likely to be attractive to trade against.
So the classification of the gap matters more than the fill statistic. A gap formed as part of a decisive, high-conviction breakout is a poor candidate for a fade, and treating all gaps as one population averages together behaviours that differ systematically.
The pattern also says nothing about cause. It reports that price covered ground it had skipped, not whether the conditions that produced the gap have changed, and a gap that filled quickly once carries no obligation to do so again.
Gap Fill FAQs
What is a gap fill in trading?
A gap fill happens when price retraces to close a prior price gap, trading back through the full range that was skipped between two sessions or bars. The gap is considered "filled" once price has traded through every price level inside that skipped range, not just touched its edge.
Why do price gaps get filled?
Gaps often form on news, earnings, or an imbalance of orders at the open, which can leave a price range with little or no trading interest behind it. As that imbalance fades and normal two-sided trading resumes, price frequently drifts or reverses back into the untraded range, closing the gap. Not every gap fills, and timing is not guaranteed.
How long does it take for a gap to fill?
There is no fixed timeframe. Some gaps fill within the same session that created them, others take days, weeks, or months, and some are never filled at all. The type of gap and the strength of the trend that produced it both influence how quickly, or whether, a fill occurs.
Does every gap eventually fill?
No. Common gaps that form in quiet, low-conviction conditions fill often, but breakaway gaps that launch a new trend and exhaustion gaps that mark a trend's final move behave differently, and a strong trend can leave a gap unfilled indefinitely. Treating "gaps always fill" as a rule rather than a tendency is a common mistake.
What is the difference between a gap fill and a gap fade?
A gap fill describes the price event itself: price trading back through the full skipped range. A gap fade is a trading approach that bets on that event happening, typically by taking a position against the direction of the gap shortly after the open in anticipation of a retrace back toward the prior close.
Is the claim that gaps always fill testable?
Only with a stated horizon. Given unlimited time, almost any price gets revisited in most instruments, so the claim is nearly unfalsifiable as usually phrased. Attached to a window, such as within twenty sessions, it becomes a measurable proposition that can be checked per instrument and per gap type. The version without a window is not a claim about markets so much as a claim about eventually.
Does a partial fill count?
That depends on a definition that is rarely given. Price can retrace most of the gap and stop short of closing it entirely, which under a strict reading is not a fill and under a loose one is. The distinction matters for anyone counting fill rates, because the two definitions produce noticeably different figures on the same data.
Which edge of the gap is the fill target?
Two conventions exist. One targets the previous session close, treating the gap as filled when price returns to where the prior period ended. The other targets the near edge of the gap, which for a gap up is the previous high. The second is reached first and is the less demanding condition, so fill statistics computed under it are higher.
Do index gaps fill differently from single-stock gaps?
They arise differently, which is the more useful observation. An index gap reflects a broad move with no company-specific information attached, while a single-stock gap often follows a repricing on new information about that company. The second involves a change in what participants believe the security is worth, which is a reason to expect different behaviour rather than a measurement of it.