What it is
The gap-fill swing is a slower cousin of the intraday gap fill. Rather than fading a gap in the first hour, it waits for evidence over one or two days that the gap has no follow-through, then enters a position aimed at the pre-gap close over the following 3 to 10 sessions. It applies to gaps caused by sympathy moves, sector news, analyst notes and other soft catalysts, not to earnings gaps, which belong to post-earnings-drift.
The logic
A gap that does not extend within two days has usually exhausted its cause. The buyers who reacted to the note or the sector move are done; the stock now has a pocket of thin volume between the gap and the pre-gap price, and holders who bought at the top of the gap are sitting on small losses with no new information to justify holding. Gaps fill because those holders sell, and because there is little natural demand in the gap's price zone until the pre-gap level, where the previous buyers live.
On the other side are traders who bought the gap as a breakout and are hoping for continuation, and the analysts' clients who bought the upgrade. When the catalyst is soft, they are the supply.
Setup rules
- Market: stocks with average daily dollar volume above $30 million, sector ETFs, index ETFs. No small caps; their gaps are too often real.
- Timeframe: daily for the setup; intraday only for execution.
- Gap conditions: an up gap of 2 to 6 percent (for shorts) not caused by earnings, guidance, M&A or FDA-type binary news; a catalyst that is either absent or soft (upgrade, sympathy, index inclusion rumour).
- Failure conditions: two full sessions after the gap without a close above the gap day's high; the second day closes in the lower half of the gap day's range; volume on days 1 and 2 declining.
- Trend context: the stock is not in a strong uptrend (below a 3-month high) and the gap did not break a multi-month base. Fading gaps out of bases loses.
- Short constraints: shares are borrowable at a reasonable rate; short-interest is below 10 percent of float to avoid squeezes.
Entry, stop, target
Short on day 3's open, or on a break of day 2's low. Stop above the gap day's high plus 0.5 ATR. Target is the pre-gap close (a full fill); a conservative version takes half at the gap's midpoint. Time stop of 10 sessions.
| Item | Level | Notes |
|---|---|---|
| Pre-gap close | 100.00 | |
| Gap-day range | 103.50 to 105.00 | Gap 4 percent, closed 104.20 |
| Day 2 close | 103.80 | Lower half, volume down |
| Entry | 103.40 | Break of day 2 low |
| Stop | 105.90 | Gap high plus 0.5 ATR, risk 2.50 |
| Target 1 | 102.00 | Gap midpoint, reward 1.40, 0.6R |
| Target 2 | 100.20 | Full fill, reward 3.20, 1.3R |
The R:R is unattractive by design; the setup is a high-win-rate trade, and it depends entirely on the classification of the gap being right. If the win rate in your own testing is not above 60 percent, the setup does not pay.
Position sizing and risk
Shorting into a gap carries squeeze risk; risk no more than 0.5 percent of equity per trade using /tools/position-size, and use a hard stop order rather than a mental one. Long versions (fading gap-downs) are easier to execute and carry gap-down-again risk instead. Read /learn/risk-management on asymmetric outcomes before running a short-biased book of these; a single squeeze can erase ten fills.
What breaks it
- Misread catalysts. A "soft" upgrade that is actually the start of a re-rating. The 2-day failure filter helps but does not eliminate this.
- Squeezes. A short into a stock with hidden demand can gap higher a second time. The stop is a real order, not a plan.
- Trending markets. In a strong bull market up-gaps in strong names extend more often than they fill; restrict to gaps in stocks that are not at highs.
- Costs. Borrow fees, the spread and the small target combine to make this a low-margin trade. The full-fill target is needed to make it work, and it is the target reached least often.
- Edge decay. Gap statistics in index ETFs have shifted as more systematic capital fades gaps; the fill rate at 5 days is lower than older studies claim.
How to test it
Scan for every gap in your universe over 5 years, manually tag the catalyst type (this is the slow, unavoidable step), and record the fill status at 2, 5 and 10 days. That gives you fill rates by catalyst type before any entry rule. Then apply the 2-day failure filter and your entry and exit rules with costs including borrow. If the fill rate for soft-catalyst gaps that failed the 2-day test is not at least 15 points higher than for all gaps, the filter is not adding value. Minimum 300 tagged gaps. Paper-trade for a quarter, since the setup is quiet outside of busy news periods.
Variations
- Gap-down long version for index ETFs and quality large caps that gap down on sector news.
- Options version: a short-dated put debit spread instead of a short stock position to cap squeeze risk; see credit-spread-program for structuring logic.
- Intraday version: see gap-and-go-gap-fill.
Further reading
gap, mean-reversion, short-selling, short-interest, short-squeeze, float, atr, win-rate, expectancy, bull-trap.
Related playbooks: gap-and-go-gap-fill, post-earnings-drift, range-mean-reversion-20ma, afternoon-reversal