Field guide / Premarket stock scanner
Make sense of the morning’s movers.
A premarket stock scanner turns overnight price changes into a list you can research. Gapperz brings the move, volume, chart, and available catalyst together so your morning starts with context.
By GapperzUpdated
Before the bell.
A focused research routine from first activity to the regular-session open.
- 04:00
Premarket begins
See which names are moving from the previous close.
- Research
Build the context
Read volume, the source behind a catalyst, and the chart.
- Monitor
Keep a focused list
Save the names and conditions you want to revisit.
- 09:30
The regular session opens
Recheck the list as participation changes.
- 01Find the names moving from the previous regular-session close.
- 02Read participation and the source behind the move alongside price.
- 03Carry a focused watchlist into the open, with clear conditions to monitor.
A gap is a starting point for research.
A premarket gap measures where a stock is trading relative to its previous regular-session close. If it closed at $4.00 and trades at $4.80 before the next open, it is up 20% from that reference. A scanner brings those changes into one sortable view.
The percentage answers a specific question: how far has the price moved from the close? The next questions are about the activity behind it. Look at how many shares have traded, when the latest trade occurred, and whether there is a company announcement or filing to read.
Gapperz’s Premarket Gappers scanner organizes names by the size of their gap in either direction. Open a result to move from the list into its chart and available symbol context. The same symbol stays at the center of the research, so you spend less time rebuilding the view.
Nasdaq lists premarket hours as 4:00–9:30 a.m. Eastern. Use that session boundary when comparing premarket volume and price levels.
Know exactly what the percentage compares.
Divide the current price by the previous close, subtract one, and multiply by 100. The reference belongs to the previous regular session. A corporate action such as a split also makes the reference-price basis important: both prices need to be comparable.
Gap percentage calculator
Try your own numbersCompare a current price with the previous regular-session close.
Change from previous close
+20.00%
Formula: (current price ÷ previous close − 1) × 100.
Illustrative inputs. This calculator measures a relationship between numbers; it does not forecast a stock’s next move.
Read the row from movement to context.
| Field | What it answers | What to check next |
|---|---|---|
| Gap % | How far is price from the previous close? | The reference price, direction, and timestamp. |
| Premarket volume | How much has traded in this session? | Whether recent activity supports the total. |
| Relative volume | How does activity compare with its usual pace? | A same-time baseline and enough historical observations. |
| Bid / ask spread | How far apart are the current quotes? | The spread relative to the stock price and quote freshness. |
| Catalyst | What source provides context for the move? | The original announcement, publication time, and company identity. |
| Chart and levels | Where has the session traded so far? | The premarket range and recent price behavior. |
Volume and relative volume work together. A large share count describes the activity already observed; RVOL compares that activity with the stock’s own history. Our relative-volume guide explains the denominator and includes a free calculator.
Read the spread beside the percentage move. Extended-hours participation is different from the regular session, and quotes can be wider. FINRA’s extended-hours explanation describes how lower liquidity affects prices and spreads.
Build your morning list in Gapperz.
Start with Premarket Gappers.
Use the gap-sorted view to find movement across the supported universe. Read the session and freshness labels before comparing rows.
Open one name and read the evidence.
Bring the chart and symbol context into view. Compare price, volume, the recent range, and any available catalyst. Follow a source link when you want the original announcement.
Save a focused watchlist.
Keep the symbols that match your research criteria together. A short list makes it easier to revisit what changed and remember why each name caught your attention.
Define the condition you want to monitor.
Set an alert for a condition you can describe, such as a price level. Choose from the delivery channels available on your plan, and keep your research attached to the symbol.
The guided product tour walks through this flow with sample data. Use it to get familiar with the workspace before your next session.
At 9:30, take a fresh look.
The opening session introduces a new reference point and a different pace of participation. Revisit the names you saved: compare the opening price with the premarket range, read the latest volume, and check whether the original catalyst has a new update.
A stock can remain far above yesterday’s close while moving lower from its morning high. That is why the gap percentage and the current intraday structure deserve separate attention. The momentum scanner guide shows how to read that distinction.
After the session, use the daily archive to revisit published scanner reports. Keeping the original time and context with a result makes the review more useful than a list reconstructed after the move.
A few useful answers.
What time does premarket scanning start?
Nasdaq’s premarket session runs from 4:00 to 9:30 a.m. Eastern on trading days. Gapperz’s extended-session volume baseline starts at 4:00 a.m. ET. Read the timestamp and session label on the data you are viewing; your broker sets its own supported trading hours.
Is the biggest gap always the most useful stock to research?
Gap size is one way to sort a list. Volume, the spread, the chart, and a dated catalyst explain different parts of the move. Compare those fields before deciding which names deserve more research time.
Can I see an example before creating an account?
Yes. The public product tour shows the scanner and linked research workspace with clearly labeled sample data. The daily archive provides published session reports. Live account access and current subscription terms are on the plans page.
Do I need a float value to use the premarket scanner?
The broad premarket workflow uses price movement and participation. It does not require a float value. Gapperz keeps unsupported float data unknown, so you can research the rest of the row without treating an estimate as a fact.
Sources & editorial notes
Prepared by Gapperz using our scanner definitions and the primary references below. The examples are illustrative; the public methodology explains how we label data and research context.