Pre-Market Gap Fill Rate

The pre-market gap fill rate measures how often a price gap opened in early morning trading (before 9:30 a.m. ET) is closed before the end of the regular session. Gaps and their fill rates vary by liquidity, volatility, and the news catalyst driving the move.

What creates a gap

A gap occurs when the opening price differs substantially from the previous close due to overnight news. An earnings surprise, a macroeconomic shock, a merger announcement, or a single large trade in after-hours or pre-market trading can move prices before the official open.

For example, a stock closing at $50 might open at $52.50 if the company announces strong earnings. That $2.50 difference is the gap. During the pre-market session (4 a.m. to 9:30 a.m. ET), buy and sell orders accumulate at the new level. When the regular session opens, the stock may continue higher, hold, or reverse back toward the previous close—or anywhere in between.

The gap fill is when the stock price returns to or passes through the previous close. If the $50 close stock gapped to $52.50 at the open, a fill would occur at any point when the stock traded at or below $50 during the day. Not all gaps fill; some persist, extend further, or close days later.

Fill rates by gap size and direction

Empirical studies of gap behavior show that smaller gaps fill more reliably than large ones. A gap of 1–2% might fill 70% of the time the same day. A gap of 3–5% fills 50% of the time. Gaps larger than 5% persist about 30–40% of the time; the market is signaling that the repricing is substantive, not purely mechanical.

The direction of the gap also matters. Bullish gaps (up gaps driven by positive news) and bearish gaps (down gaps driven by negative news) have similar fill rates overall, but the nature of the catalyst influences persistence. A gap caused by a large single trade in low-liquidity pre-market activity often fills quickly once regular session liquidity arrives. A gap caused by material news—a dividend cut, a lawsuit, a regulatory change—is more likely to persist or extend further.

Liquidity as the primary determinant

The single strongest predictor of gap fill rate is stock liquidity. High-volume, tight-spread names like mega-cap technology and financial stocks have pre-market gaps that fill 60–75% of the time. Micro-cap or illiquid stocks show fill rates as low as 20–30%.

Why? Large-cap stocks attract algorithmic and human traders across the full pre-market and regular session. If the move seems overdone, traders arbitrage it. The tight bid-ask spread makes round-trip transactions cheap. A gap from $50 to $52 in a liquid name is quickly closed by buyers willing to lock in profits and sellers ready to establish positions at the new price.

Conversely, a gap in a stock with a $1 wide bid-ask spread and minimal after-hours volume cannot be efficiently filled. The cost of trading the round-trip to close the gap exceeds the profit, so traders leave it alone. The gap persists or closes slowly as the regular session volume allows.

Earnings-driven gaps are sticky

Gaps driven by quarterly earnings reports behave differently from gaps driven by brief news or pre-market quirks. An earnings surprise is a change in fundamental expectations, and the market reprices gradually as new information flows and positions are established.

A stock that gaps 8% on better-than-expected earnings will rarely fill that gap the same day. The repricing is real; the margin-of-safety traders require at the old price no longer applies. Fills may occur days, weeks, or months later if the earnings surprise disappoints later or if the market rotates. But the same-day fill rate is low—perhaps 10–20%.

In contrast, a stock that gaps 3% on a rumor that is later refuted, or on a single large pre-market order that moves the bid, often fills within hours once the regular session volume clarifies sentiment.

Time decay and intraday closing

Gaps that do fill typically close in the first 1–3 hours of the regular session. Intraday momentum traders lean on this: if a stock gapped up 2% on light news, short-term sentiment favors a reversal within the first hour.

However, liquidity dries up as the session progresses. If a gap has not filled by mid-session, it is less likely to fill the same day. By late afternoon, the traders who would arbitrage small mispricings have reduced size, and the remaining bid-ask spread widens. A gap that persists into the final hour often carries overnight, filling (or not) the next day.

Volatility amplification

High historical volatility stocks experience larger gaps and lower fill rates. A highly volatile name can gap 5% and then move another 5% during the session, never reverting. Gaps in low-volatility stocks (utilities, consumer staples) are smaller and fill more readily.

This makes intuitive sense: volatility reflects uncertainty about fair value. A wide range of opinions means the post-gap price may be as legitimate as the pre-gap price. Traders in high-vol names hold more diverse views and are less inclined to collectively arbitrage the gap away.

Practical implications for traders

Day traders and scalpers exploit gap-fill patterns by fading (betting against) gaps that are statistically likely to close. A trader sees a stock gap up 2% on modest news and enters a short position, targeting the previous close. With a tight bid-ask spread and high liquidity, this is a reasonable statistical edge.

However, the edge disappears if the catalyst is fundamental. A trader betting on a gap fill must distinguish between noise (a pre-market spike that reverses) and signal (a genuine repricing). Earnings gaps, in particular, are poor candidates for gap-fade trades; the new price may be here to stay.

The gap fill rate also matters for position traders who are long or short and worry about reversals. A trader bullish on a stock that gaps up may worry the gap will fill, creating a false breakout. Understanding the fill-rate baseline for that stock’s liquidity and the catalyst type helps calibrate the risk.

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