Price Gaps Explained

At a glance

What a gap is: An open materially away from the prior close
Main cause: Information arriving while the market is closed
Key risk: Stops do not execute during a gap
Main classifier: Whether a genuine catalyst exists

Key takeaways

Gaps occur because information arrives while trading is suspended, so the market reopens at a new equilibrium price.
Gaps with genuine catalysts and heavy volume tend to continue; gaps without catalysts and on thin volume tend to fill.
Overnight gap risk is the primary reason swing trading positions must be smaller than the stop distance alone would suggest.
Holding a position through an earnings report exposes you to a gap several times larger than your intended risk.
In 24-hour markets true gaps are rare, but weekend repricing produces the same effect.

The four gap types

Type	Context	Typical behaviour	How to identify
Common gap	Within a range, no catalyst	Fills quickly	Small, low volume, no news
Breakaway gap	Out of a base or range, with news	Continues; rarely fills soon	Large, very high volume, clear catalyst
Runaway / continuation gap	Mid-trend, accelerating	Continues, often marks the midpoint	Occurs within an established move
Exhaustion gap	After an extended move, climactic	Reverses	Very high volume, then immediate weakness

The classification is only fully clear in hindsight, which is a limitation worth acknowledging. In real time, the usable discriminators are the presence of a catalyst, the relative volume, and where the gap occurs within the larger structure.

Do gaps fill?

The claim that all gaps eventually fill is unfalsifiable over an infinite horizon and useless in practice. The meaningful question specifies both the window and the gap type.

Small gaps fill more often than large ones. A gap of less than half the average daily range frequently closes within the session.
Gaps without catalysts fill far more often than gaps with confirmed news. This is the single strongest discriminator.
Index ETF gaps fill more reliably than single-stock gaps, because indices lack company-specific information shocks.
Counter-trend gaps fill more often than gaps in the direction of an established trend.
High relative volume reduces fill probability, because it indicates genuine repositioning rather than thin repricing.
Earnings gaps frequently do not fill for months, and gap continuation is the basis of post-earnings drift strategies.

The practical implication for trading gaps is covered in the gap trading strategy guide. The implication for risk management is more important for most traders and is covered below.

Gap risk: the limit of stop losses

A stop-loss order becomes a market order when triggered. If the market gaps past the stop level while closed, the order executes at the opening price, which can be far worse than intended.

Planned trade:
   Entry 68.00,  stop 64.60 (5% below),  risk 1% of equity
   Account 50,000 -> risk 500 USD -> 147 shares

Earnings report after the close.  Stock opens at 52.00.

   Actual loss = 147 x (68.00 - 52.00) = 2,352 USD
               = 4.7% of the account
               = 4.7 times the intended risk

The stop did not fail.  It executed correctly, at the first
available price.  There was simply no price between 64.60
and 52.00 at which anyone was willing to trade.

How a gap turns a planned loss into an unplanned one.

Managing gap risk systematically

1
Track earnings dates for every position
The most common avoidable source of large gaps. Exclude candidates reporting within the expected holding period, or close before the report.
2
Cap position notional, not just risk
10 to 20 percent of equity per position regardless of how tight the stop is.
3
Diversify across sectors and factors
Company-specific gaps are independent; macro gaps are not. Sector limits prevent a single event from gapping five positions at once.
4
Model gaps in your backtest
Test what happens if 2 percent of trades gap through the stop by three times the intended risk. If that breaks the strategy, position sizes are too large.
5
Consider defined-risk alternatives
For event exposure, options cap the loss at the premium, which removes gap risk entirely at the cost of the premium.
6
Reduce size into known event windows
Central bank decisions, elections, and major data releases all produce gap risk in macro-sensitive instruments, not just in single stocks.

Gaps by market

Market	Gap frequency	Main cause	Mitigation
Individual stocks	High	Earnings, guidance, M&A, regulatory	Avoid events; cap notional
Index ETFs	Moderate	Overnight macro moves	Smaller effect; diversified by construction
Futures	Low	Nearly 24-hour trading; weekend and holiday gaps	Reduce size into weekends
Forex	Low	Weekend open after news	Reduce size or flatten into the weekend
Crypto	Very low	Continuous trading; outage-driven gaps only	Venue risk rather than gap risk
Options	Inherits the underlying	Underlying gaps plus volatility changes	Defined-risk structures cap the loss

The table explains part of the appeal of futures for systematic traders: near-continuous trading substantially reduces the gap exposure that dominates single-stock swing trading, though it does not eliminate weekend risk.

Frequently asked questions

Do all gaps get filled eventually?

Over an unlimited horizon the claim is unfalsifiable and useless. Within any practical window, fill rates depend on gap size, whether a catalyst exists, and the instrument. Small gaps in index products without news fill often; large earnings gaps in single stocks frequently do not fill for months or at all.

How do I protect against overnight gaps?

You cannot prevent them, only limit their impact. The controls are avoiding known events such as earnings, capping position notional as a percentage of equity, diversifying across sectors, and using defined-risk option structures when you want event exposure. Stop orders provide no protection during a gap.

What causes a gap in a 24-hour market?

Weekend closures, exchange outages, and trading halts. Futures and forex gap at the weekly open when news arrives while markets are shut. Crypto trades continuously, so true gaps are rare and usually reflect an exchange being unavailable rather than the market pausing.

Should I trade the gap fill?

Only with strict filters: no catalyst, moderate gap size, low relative volume, a liquid instrument, a hard stop, and a midday time stop. Without those, fading gaps means taking countertrend positions into news, which produces occasional very large losses.

Why did my stop fill so far below my stop price?

Because a stop order becomes a market order when triggered, and it executes at the first available price. If the market opened well below your stop, there was no trading between your stop level and the opening price. The order worked as designed; the protection simply does not exist across a gap.

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Referenced by

Educational use only. This guide explains how a strategy works. It is not investment advice, not a recommendation, and no result described here is a forecast. Test any approach on historical and out-of-sample data, size positions conservatively, and never risk money you cannot afford to lose.