A gap up in stocks is an opening price substantially higher than the previous regular-session close. If a stock closes at $50 and opens at $55 the next trading day, it has gapped up by 10%.
On a chart, a gap up may appear as an empty space between the previous close and the new opening price. No regular-session trades occurred at the prices inside that range. Nasdaq calls this a "gap opening" and notes that unusually positive news can cause one.
Gap Up Example
The gap-up percentage is calculated as follows:
Gap-up percentage = (Opening price − Previous closing price) ÷ Previous closing price × 100
| Previous close | Next opening price | Gap-up percentage |
|---|---|---|
| $50 | $55 | 10% |
| $100 | $108 | 8% |
| $25 | $27.50 | 10% |
A gap up is often viewed as a bullish opening signal, but it does not show that the stock will keep rising.
Why Do Stocks Gap Up?
A stock can gap up when new information changes how buyers value the company before the regular market opens. Common catalysts include:
- Better-than-expected earnings
- Higher revenue or profit guidance
- FDA approval or other regulatory news
- A merger or acquisition announcement
- An analyst upgrade
- Strong news affecting the industry or wider market
- A major contract or product announcement
- Short sellers buying shares to close positions
Nasdaq identifies unusually positive news as one reason for a gap opening. The gap reflects the difference between the previous close and the price at which buyers and sellers are willing to trade when the next regular session begins.
Is a Gap Up the Same as a Stock Rising in Premarket Trading?
No. A stock can rise in premarket trading without producing a large gap up at the regular-session open.
For U.S. stocks, the regular trading session generally runs from 9:30 a.m. to 4:00 p.m. Eastern Time. Traders usually measure a gap up by comparing the previous regular-session close with the next regular-session opening price. After-hours prices are reported separately and may differ between market-data providers.
For example:
- Previous regular-session close: $50
- Premarket price: $55
- Regular-session open: $52
The regular-session gap up is 4%, not 10%, because the calculation uses the $52 opening price.
What Does a Gap Up Indicate?
A gap up indicates that overnight buying interest or new information has changed short-term price expectations.
1. The Catalyst
A gap linked to strong earnings, regulatory news or a major business announcement may draw more attention than a gap with no identifiable reason.
2. Trading Volume
Higher-than-usual volume shows that more investors are participating in the move. A gap on light volume may be less convincing, especially in a thinly traded stock.
3. Price Action After the Open
A stock that stays above its opening price may have stronger short-term demand. If it quickly falls toward the previous close, traders may call the move a gap fade. This means the initial upward move is losing momentum.
What Is a Gap Fill?
A gap fill occurs when a stock later moves back into the price area created by the gap. Traders may use the term when the stock returns to the previous closing price.
In the $50-to-$55 example, the gap is $5. If the stock later trades back to $50, traders would commonly describe the gap as filled.
A gap does not have to fill, and its timing cannot be predicted from the gap alone. Some gaps reverse quickly. Others remain open for a long time.
Gap Up Versus Gap Down
| Term | Meaning |
|---|---|
| Gap up | The stock opens above the previous regular-session close |
| Gap down | The stock opens below the previous regular-session close |
| Gap-and-go | The stock gaps up and continues moving higher after the open |
| Gap fade | The stock gaps up but then reverses lower |
| Gap fill | The stock returns into the price range created by the gap |
What Are the Risks of Trading a Gap Up?
A gap-up stock can be volatile. Its price may move before an order reaches the market. A market order guarantees execution, but not a specific execution price.
Stop orders have a related risk. When triggered, a stop order becomes a market order, so the final execution price can differ significantly from the stop price in a fast-moving market.
Premarket and after-hours trading can also have different levels of liquidity, accepted order types and market-maker participation. As a result, extended-hours prices may not reflect the regular-session market as closely.
Bottom Line
A gap up shows that overnight news or buying interest changed the stock's opening price. It can point to momentum, but it is not automatically a buy signal. The catalyst, trading volume, post-open price action and order-execution risks all matter.