Gap Fill¶
A gap fill occurs when price retraces back through the range skipped during an overnight or intraday gap, closing the void left on the chart. A gap forms when a security opens with no price overlap to the prior session's trading range. A full fill is confirmed when price trades at or below the prior session's close (for gap-ups) or at or above it (for gap-downs); a partial fill enters the gap zone but reverses before completing it.
HOW IT WORKS¶
A gap is defined by two boundaries: the prior session's close and the opening price of the new session. Gap size is calculated as:
Gap Size (%) = |Open − Prior Close| / Prior Close × 100
Fill probability varies by gap type. Common gaps fill quickly and frequently. Breakaway gaps, driven by genuine catalysts such as earnings beats or acquisitions, often never fill. Runaway gaps form mid-trend and fill inconsistently. Exhaustion gaps signal trend reversal and tend to fill fast. The blanket rule that "all gaps fill" is a misconception — unfilled gaps on high-conviction catalysts are common across large-cap equities.
IN TAPEBOARD¶
Tapeboard marks gap zones directly on the price chart so traders can identify fill levels without manual calculation. When a security opens with a qualifying gap, the terminal highlights the gap zone and plots the prior session's close as the confirmed fill level. Traders running gap-and-fade setups can use these levels as price targets, while those monitoring gap-and-go failures can set alerts at the gap boundary to flag when price re-enters the zone. Unfilled gaps from prior sessions remain visible on the chart as persistent support and resistance references.