Gap Fill

What is a Gap Fill?

A gap fill is the return trip. After price gaps away from a prior reference, it later trades back through the untraded span until the gap is closed, conventionally when price touches the pre-gap reference (for an opening gap, the prior session's close). A partial fill covers only part of the span, and many traders track the gap's halfway point as an intermediate reference.

Fill behavior is the sorting mechanism of gap taxonomy. Gaps that fill quickly and quietly get classified after the fact as common gaps, while gaps that stay open as price runs are the signature of breakaway and continuation moves. Whether a given gap fills is not knowable in advance: fill frequency varies with gap size, direction, and market regime, and the folk rule that every gap eventually fills is not a law.

How traders use it

• In gap-fade strategies: intraday traders fade opening gaps toward the prior close, using the full fill as the target and filtering by the gap's size relative to recent average range; large news-driven gaps are commonly excluded on the view that they trade more like breakaway gaps than common ones.
• As a magnet and target: an open gap above or below price provides an objective reference, so swing traders use the pre-gap close, or the gap midpoint for partial fills, as profit targets when price rotates back toward the span.
• As a strength read: a gap that refuses to fill on the first retracement attempt suggests initiative conviction behind the move, while an immediate full fill files the gap under noise and weakens any breakout thesis built on it.