Insights from ChartsWatcher
Gap Percentage vs Change From Open: Why Scanners Show Different Results
Gap percentage measures the move from the previous close to the opening price. Change from open measures the move after that opening price. A stock can have a large positive gap while falling throughout the regular session.
One stock, three different percentages
Suppose a stock closed yesterday at $10, opened today at $12, and now trades at $11.
| Measurement | Calculation | Result |
|---|---|---|
| Opening gap | (12 − 10) ÷ 10 × 100 | +20% |
| Change from open | (11 − 12) ÷ 12 × 100 | −8.33% |
| Current change from previous close | (11 − 10) ÷ 10 × 100 | +10% |
All three are correct. They use different reference prices. A “top gapper” therefore need not be a stock moving upward since the open.
Choose the reference that matches the question
Use an opening-gap measurement to research the difference between consecutive sessions. Use change from open to describe the move since today's regular-session opening price. Use current change from previous close when you want the latest price relative to yesterday's close.
ChartsWatcher's Gap from close reference defines the opening-gap comparison. Change from open is a separate filter. Both offer dollar and percentage options; make sure a copied threshold uses the intended units.
Premarket needs special care
Before the regular session opens, today's regular-session opening price does not yet exist. A scanner labelled “premarket gap” may instead compare the current premarket price with the previous close. That is not the same measurement as the completed opening gap.
ChartsWatcher's Change from open documentation says it uses yesterday's opening price during premarket. Do not interpret that value as today's move from a regular-session open. Check the session-specific definition rather than assuming a familiar label means the same thing everywhere.
A practical configuration check
Write down three items before building the scan:
- The reference price: previous close, today's open or another session-specific value.
- The comparison price: current price or opening price.
- The session and units: premarket or regular hours; dollars or percent.
Then verify one matching symbol manually on a chart. This catches a reference-price mismatch much faster than adjusting several thresholds at once.
Explore the scanner directory to compare different views of market movement. A gap or percentage change describes what happened; neither establishes that the move will continue or reverse.