Understanding Price Gaps: Overnight News and the Gap-Fill Myth
Learn why stock prices jump between trading sessions, how to identify three key gap types, and why waiting for gaps to fill can be costly.
Indian stock markets trade from 9:15 AM to 3:30 PM. But business does not stop when the closing bell rings. Earnings reports drop at 7:00 PM, central banks make announcements overnight, and global commodity prices swing while you sleep. When the market reopens next morning, the opening auction reprices the stock instantly to reflect this new reality. The chart literally skips steps, creating an empty space between yesterday's price range and today's open. This visual empty space is called a gap.
Why Gaps Happen: The Pre-Open Auction
A gap does not mean trades occurred in thin air. It means buyers and sellers agreed during the 15-minute pre-open session that the old price was entirely obsolete. If a pharmaceutical firm reports a surprise quarterly profit after hours, no shareholder will sell at yesterday's close of ₹500. Buyers must bid ₹530 or higher just to find a willing seller. The first trade prints at ₹530, leaving a ₹30 blank zone on the daily chart.
Three Distinct Types of Gaps
Not all gaps mean the same thing. Chartists generally classify them into three functional categories based on where they appear within a broader trend:
- Common Gap: Appears inside a boring, sideways trading range. Volume is usually ordinary. It reflects minor overnight noise and tends to close quickly.
- Breakaway Gap: Occurs when price decisively jumps out of a long consolidation zone or beyond a major support/resistance boundary on heavy volume. It signals the start of a fresh, aggressive trend.
- Exhaustion Gap: Appears after an extended, weeks-long rally or steep decline. It represents a final burst of emotional buying or panic selling. Price usually reverses within a few sessions, signaling trend fatigue.
The Gap Fill: Magnet Myth vs Base Rate
A popular market myth claims that all gaps must be filled. A gap is considered 'filled' when future price action trades all the way back through the empty price zone to touch the previous day's high (in an upward gap) or low (in a downward gap).
The idea that gaps act like cosmic magnets pulling price back is dangerous. While common gaps in sleepy ranges do fill often (a high base rate of filling), powerful breakaway gaps often stay unfilled for months or even years. Waiting for a fast-growing company's breakaway gap to fill before buying often means watching a multibagger run away forever.
- Step 1: Identify Day 1 High = ₹400 (yesterday's peak price before market close).
- Step 2: Identify Day 2 Low = ₹425 (today's lowest traded price after a big overnight gap up).
- Step 3: Measure the Gap Size: ₹425 - ₹400 = ₹25 unfilled window.
- Step 4: Determine the Fill Target: For the gap to fully fill, price must fall from ₹425 back down to touch ₹400.
- Outcome: If heavy institutional volume accompanied the jump to ₹425, treating ₹400 as a guaranteed retracement target is a statistical trap.
Context matters more than the gap itself: common gaps fill easily because nothing fundamental changed, but genuine breakaway gaps represent permanent repricing that the market has no obligation to undo.
You can inspect historical daily candlestick charts and volume spikes on any company's technical analysis page on stock-analyze.com to see whether past gaps acted as durable support or filled immediately.