What it is
A gap is an open away from the prior close. Gaps come in two very different species. Gap and go is a momentum trade on a gap caused by a real catalyst (earnings, guidance, a contract, a macro print) that holds its first pullback and continues. Gap fill is a mean-reversion trade on a gap without a durable catalyst, which drifts back toward the prior close as the opening excitement fades. The whole skill is deciding, in the first 15 minutes, which one you are looking at.
The logic
A catalyst gap represents new information, and the market rarely prices new information fully at the open. Analysts revise, funds re-underwrite, and short sellers cover over hours and days, so the gap extends. A non-catalyst gap represents an imbalance of overnight orders, not information, and once those orders are filled there is nothing holding price away from where the market last agreed on value.
Who is on the other side? In gap and go, it is early profit takers and fade traders who are betting on a fill. In gap fill, it is the people who bought the open on excitement, and their stops sit just under the opening low. The setup you pick determines whose stops you are aiming for.
Setup rules
- Market: stocks with average daily volume above 1 million shares and a price above $5; index ETFs for gap fills. Low-float names gap more but fill less predictably.
- Timeframe: 1-minute for the first 15 minutes, 5-minute afterward.
- Gap and go conditions: gap of at least 3 percent (stocks) or 0.5 ATR (indices); a named catalyst; pre-market volume above 20 percent of average daily volume; the first 5-minute pullback holds above the vwap and above the pre-market low.
- Gap fill conditions: gap between 0.5 and 2 percent with no catalyst; opening 5-minute bar closes back toward the prior close; relative-volume below 1.0 after the first 15 minutes. Weak volume is the tell.
- Avoid gaps larger than 10 percent for either mode; those are their own regime and belong to post-earnings-drift.
Entry, stop, target
Gap and go: buy the break of the first pullback high on the 5-minute chart, stop below the pullback low, target the gap height projected from the open (a measured move) and then the daily atr.
Gap fill: short below the opening 5-minute low (for an up gap), stop above the opening high, target the prior close. The prior close is a hard target because the fill is the thesis; do not hold for more.
| Item | Gap and go (long) | Gap fill (short) |
|---|---|---|
| Prior close | 40.00 | 40.00 |
| Open | 42.00 (5 percent gap) | 40.60 (1.5 percent gap) |
| Entry | 42.40 | 40.45 |
| Stop | 41.80 (risk 0.60) | 40.75 (risk 0.30) |
| Target | 44.00 (reward 1.60, 2.7R) | 40.05 (reward 0.40, 1.3R) |
Gap fills are lower R:R with a higher win-rate; gap and go is the reverse. Neither number is stable across regimes.
Position sizing and risk
Gap trades happen at the most illiquid, widest-spread moment of the day, so risk 0.25 to 0.5 percent of equity rather than a full 1 percent, and size from the stop distance with /tools/position-size. Cap gap trades at two per day, and never add to a gap fill that is moving against you; the whole point of the setup is that the opening move can be wrong, and that includes yours. The daily loss limits in /learn/risk-management apply with extra force here.
What breaks it
- Misclassifying the gap. The dominant failure mode is treating a catalyst gap as a fill candidate and shorting into a squeeze. Read the news before the open, every time.
- Halts. Stocks gapping on news can be halted; you cannot manage a stop inside a trading-halt.
- Spreads and slippage. In the first five minutes the spread on a mid-cap can be ten times its normal width. Limit orders only.
- Edge decay. Gap fill statistics for index ETFs have weakened as more systematic funds trade them; the naive "all gaps fill" claim is false and has been for years. Gap and go survives better because it depends on information, not on a pattern.
- Drawdowns. Expect losing streaks of 6 to 8 in gap and go; the wins are lumpy.
How to test it
Scan for every gap above your thresholds over two years of daily data, tag each with catalyst or no catalyst by reading the news headline of the day (tedious, necessary), and record whether the gap held its first pullback and whether it filled by the close. That gives you base rates before you add any entry rule. Then replay 100 qualifying gaps of each type with your exact entries and record r-multiple and adverse excursion. If your gap fill win rate in testing is above 70 percent, be suspicious; it is probably a look-ahead error.
Variations
- Partial gap fill: target only half the gap for a higher win rate.
- Gap and go with ORB: use opening-range-breakout rules for the entry.
- Pre-market range break: enter on the break of the pre-market high rather than the first pullback, which is earlier and riskier.
Further reading
gap, extended-hours, relative-volume, float, short-interest, trading-halt, vwap, atr, mean-reversion, dead-cat-bounce.
Related playbooks: opening-range-breakout, gap-fill-swing, post-earnings-drift, momentum-ignition-volume