A gap-up is an overnight repricing: news lands while the market is closed, buyers line up in the premarket session, and the stock opens far above yesterday's close without ever trading at the prices in between.
The day's biggest movers are usually visible by 7 or 8 a.m. — they are the stocks gapping on volume. The open is when the crowd arrives; the preparation happens before it.
Three questions separate a tradable gap from a trap. Is there a real catalyst — earnings, an approval, a contract — or just a vague press release? Is premarket volume heavy, showing genuine participation? And does the float explain the size of the move?
A gap on real news, heavy volume, and a reasonable float can trend all day. A gap on thin volume and no news is usually sold into at the open — the classic gap-and-fade.
A simple premarket routine: scan the top percentage gainers with meaningful premarket volume, attach the catalyst to each one, note the float, and mark yesterday's high and the premarket high as key levels.
By 9:25 you have a watchlist of three to five names you understand, instead of chasing whatever spikes at 9:31. This preparation is exactly what scanner tools automate — surfacing gappers, volume, float, and headlines in one view before the open.
Most brokers offer premarket from 4:00 a.m. ET, with activity concentrating between 7:00 and 9:30 as news and volume build toward the open.
Premarket liquidity is thin, so early enthusiasm can overprice the news. When full liquidity arrives at 9:30, sellers into strength often outweigh new buyers unless the catalyst is strong.
Price retracing to yesterday's close, "filling" the empty space on the chart. Weak gaps fill quickly; strong gaps may never fill at all.
TheScanner watches premarket gappers, unusual volume, whale flow, insider buying, and news catalysts across the whole market — and logs every alert so the track record is verifiable. Research tool, not investment advice.
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