Gap Risk When A Market Reopens

Price charts appear continuous, but trading is not. The gaps between sessions are where a meaningful share of price movement actually occurs.

Why prices jump rather than travel

Information arrives around the clock while trading occurs during defined hours, so news between sessions accumulates until the market can respond.

Company results are frequently released outside regular trading hours precisely so that the information can disseminate before continuous trading resumes.

The next opening therefore reflects an adjustment made in one step, with no trading having occurred at the intervening prices. The opening auction gathers accumulated orders and settles on a single price, which is where the whole adjustment lands.

What this does to stop orders

A stop order becomes active when a security trades at or through a stated price, and then executes at whatever the market offers.

If the opening price is far below the stop level, the order activates and executes at the opening price rather than at the stop.

The protection assumed was continuous trading through the level, which is exactly what a gap removes. A stop-limit order avoids selling below a stated price but may simply not execute, which trades one exposure for another.

Extended hours are not a solution

Trading outside regular hours exists but takes place with far fewer participants, wider spreads and thinner depth.

Prices established in those sessions can differ substantially from where the security opens once regular trading begins.

Executing in that environment often costs more than waiting, which is why extended-hours access rarely helps an individual acting on overnight news.

Weekend and holiday exposure

The gap grows with the length of the closure, so weekends and holiday breaks accumulate more unpriced information than an ordinary overnight.

Markets that trade continuously across time zones price developments as they occur, which is why currency and futures markets often indicate direction before equities open.

Those indications are prices in their own markets rather than forecasts of the equity opening, though they are frequently reported as the latter.

What follows for position sizing

Since exit levels cannot be guaranteed, risk has to be managed through how much is held rather than through where an exit is placed.

A position sized so that a substantial overnight move is tolerable does not depend on an order executing at any particular level.

This is the general form of the point: mechanisms that rely on trading continuing are unreliable exactly when trading stops.