Trading Halts: Limit States, Pauses and Reopening

A halt is a sequence, not a switch

Price charts flatten the event. A stock trades, then it does not, then it trades again at a different price. The rulebook underneath that flat line is a set of steps with timings attached, and the timings explain most of what a trader observes.

The mechanism is the Limit Up/Limit Down plan, approved by the SEC as a pilot in 2012 and as a permanent rule in 2019. It is administered by an operating committee whose participants are the exchanges and FINRA, and it is filed with the SEC under Section 11A of the Exchange Act.

Step one: the band

The plan “is designed to prevent trades in NMS Stocks from occurring outside specified price bands, which are set at a percentage level above and below the average reference price of a security over the preceding five-minute period.”

The reference price is defined precisely: “the arithmetic mean price of Eligible Reported Transactions over the prior five minute period.” The first reference price of the day is the primary market’s opening price, or the previous day’s closing price or last sale if the stock opens on a quote. If no eligible trades have occurred in the prior five minutes, the previous reference price stays in effect. It is updated after 30 seconds only if a new reference price would be at least 1 per cent away from the current one.

That last condition is worth pausing on. The reference price is deliberately sticky: it does not chase every print, only a move of at least one per cent. A band built on a sticky reference is therefore not a volatility forecast — it is a boundary around a slow-moving average.

The percentage parameter depends on the security and the price:

The plan adds a time condition that catches people out: “Price Bands are doubled during last 25 minutes of the regular trading day for all Tier 1 Securities and for Tier 2 Securities below $3.00.” The widening is intentional. A closing auction can move a stock quickly, and a band that was appropriate at 11 a.m. would produce repeated pauses in the last half hour.

Step two: the limit state

When a quote reaches a band, the market does not stop. It enters a state.

The plan describes the transition in two parts. When the national best bid or offer is outside the band, “the SIPs disseminate the National Best Bid (Offer) with an indicator identifying it as unexecutable.” Trading enters a limit state “if the National Best Offer (Bid) equals but does not cross the Lower (Upper) Price Band”, and the SIPs then mark it as a limit state quotation.

The distinction between “outside” and “equals but does not cross” is the whole mechanism. A quote beyond the band is shown but cannot trade; a quote exactly at the band is the trigger for the limit state clock.

Step three: fifteen seconds, then five minutes

The limit state has a deadline. “Trading exits a Limit State if, within 15 seconds of entering the Limit State, all Limit State Quotations are executed or canceled in their entirety.”

If the market does not clear within those fifteen seconds, “the primary listing exchange declares a five-minute Trading Pause. The Trading Pause may be extended for another five minutes. Thereafter, all markets may resume trading.”

Three things follow from that sentence:

1. The pause is declared by the primary listing exchange, not by each venue independently. That is what makes the halt consistent across markets.
2. Five minutes is a minimum, not a fixed duration. The pause can be extended once.
3. Resumption is not continuous trading. The reopening is handled through the exchange’s own procedures, which is why the first print after a halt can be well away from the last print before it.

The awkward middle: a straddle state

Not every deviation produces a limit state. The plan defines a separate condition: “A Straddle State occurs when the National Best Bid (Offer) is below (above) the Lower (Upper) Price Band and the NMS Stock is not in a Limit State.”

The example in the plan is concrete. If the lower band is $9.50 and the upper band is $10.50, a stock with a best bid below $9.50 and a best offer above $9.50 is in a straddle state — the bid is unexecutable, but the offer is not at a band, so no limit state has begun.

The consequence is discretionary rather than automatic: “If an NMS Stock is in a Straddle State and trading in that stock deviates from normal trading characteristics, the primary listing exchange may declare a Trading Pause for that NMS Stock.” May, not must. That is the one place in the sequence where judgement enters.

When the whole market halts

Single-stock halts are one mechanism. Market-wide circuit breakers are a different one, triggered by an index rather than a security.

The thresholds are set at three levels, measured by a single-day decline in the S&P 500 from the prior day’s close: 7 per cent (Level 1), 13 per cent (Level 2) and 20 per cent (Level 3). The filing that describes them states the operating rules: “A market decline that triggers a Level 1 or Level 2 halt after 9:30 a.m. and before 3:25 p.m. would halt market-wide trading for 15 minutes, while a similar market decline at or after 3:25 p.m. would not halt market-wide trading.” Level 1 and Level 2 “may occur only once a day”, and “a market decline that triggers a Level 3 halt at any time during the trading day would halt market-wide trading for the remainder of the trading day.”

A later exchange filing shows how the resumption mechanics are being adapted to longer trading days: after a Level 3 halt, trading “will resume the following trading day at 4 a.m. during the Pre-Market Session.” The point of that detail is that a Level 3 halt is not an intraday pause — it ends the day, and the next day begins in a session that has no price bands.

What a halt does to a resting order

A halt does not preserve the book as it was. Venues apply their own rules to orders during the pause: some queue new orders, some reject them, and cancels may be processed or held depending on the venue’s configuration.

The reopening is an auction. That means the price is determined by the orders that participate in the reopening, not by the last trade before the halt. A stop order that would have triggered on the pre-halt price does not necessarily trigger at the reopening price, and a limit order that was marketable before the halt may not be marketable after it.

The practical implication is the same one that applies to gaps in any market: the halt protects the market from trading at a price far outside a band, and it does not protect an individual order from being repriced by the event that caused the halt.

Why the sequence matters more than the headline

Most coverage of a halt reports the trigger — a 7 per cent decline, a stock down 40 per cent, a pending news release — and stops there. The mechanics explain what happens next, and the mechanics are where an order’s outcome is decided.

The band is built on an average, the limit state is a fifteen-second clock, the pause is five minutes that can be extended, and the reopening is an auction. None of those steps is designed to give a trader a better price. They are designed to give the market a chance to find one.

Risk note. The band parameters, limit state rules and pause timings in this article were read from the LULD plan; the circuit-breaker thresholds and windows from the NYSE Rule 7.12 filing; and the Level 3 resumption language from the MEMX Rule 11.23(b)(2) filing, all on 2026-10-27. Exchange rules change and venue order handling differs. Nothing here is investment advice.