The US Market-Wide Circuit Breaker (MWCB) halts trading in all US-listed stocks when the S&P 500 index falls 7%, 13%, or 20% from the prior day’s closing price, under NYSE Rule 7.12, which governs this mechanism today. This threshold is recalculated every morning, and each level triggers a pause of different length, according to the reference document published by the NYSE.
Three thresholds calculated daily from the prior close
The mechanism rests on three decline levels, all measured as a percentage against the S&P 500’s closing price from the prior session. The NYSE states it this way: “A MWCB can be triggered at three circuit breaker thresholds measured by a decrease against the prior day’s Closing Price of the S&P 500 Index — 7% (Level 1), 13% (Level 2), and 20% (Level 3)”. In practice, the index-point values corresponding to 7%, 13%, and 20% are recalculated every morning from the prior day’s close, since they depend directly on that reference level.
Different trigger windows depending on the level
Levels 1 and 2 cannot trigger a halt at any point in the trading day. The NYSE specifies that “Level 1 and Level 2 can be triggered between 9:30 a.m. and 3:25 p.m. Level 3 can be triggered at any time”. In other words, if a 7% or 13% drop occurs after 3:25 p.m. New York time, the corresponding halt does not trigger; only Level 3, the most severe, remains active at any point in the session.
Pause durations that depend on the level reached
The length of the trading halt differs sharply depending on which threshold is breached. Still according to the same NYSE document, “Level 1 and Level 2 breaches halt trading for a minimum of 15 minutes. Level 3 breach halts trading for the remainder of the trading day”. A 7% or 13% drop therefore suspends trading for at least fifteen minutes before reopening, while a 20% drop halts trading for the rest of the day, with no possible reopening before the next session.
The rule also limits how many times the first two levels can trigger in a single day. The NYSE states that “a Level 1 and Level 2 breach can be triggered only once per trading day”. Only one Level 1 trigger and one Level 2 trigger are therefore possible within a single session; only Level 3 ends trading without this limit, since it directly closes out the day.
Effects that reach beyond the stock market alone
A MWCB trigger does not affect only the stocks themselves. The NYSE specifies that “If the equities market triggers a MWCB halt, the NYSE Arca Options and NYSE American Options markets will halt trading. Any trades that occur after the halt is triggered will be nullified”. The linked options markets, NYSE Arca Options and NYSE American Options, therefore halt at the same time as the equities market, and any trade executed after the trigger moment is nullified, regardless of platform.
A 2012 reform that tightened thresholds and shortened pauses
The current thresholds of 7%, 13%, and 20% were not the first adopted by the SEC. The US regulator explains it made a methodology change in 2012: “Reducing the market decline percentage thresholds needed to trigger a circuit breaker to 7, 13, and 20 percent from the prior day’s closing price, rather than declines of 10, 20, or 30 percent”. The thresholds were therefore lowered, making the mechanism more sensitive to less extreme declines than before.
The same reform also shortened the duration of pauses that do not close the market for the day. The SEC states it proceeded by “shortening the duration of trading halts that do not close the market for the day to 15 minutes, from 30, 60, or 120 minutes”. Level 1 and Level 2 pauses, which could formerly last up to two hours, have thus been limited to fifteen minutes since this reform.
| Level | Decline threshold | Trigger window | Pause duration |
|---|---|---|---|
| Level 1 | 7% | 9:30 a.m. to 3:25 p.m. (New York time) | 15 minutes minimum |
| Level 2 | 13% | 9:30 a.m. to 3:25 p.m. (New York time) | 15 minutes minimum |
| Level 3 | 20% | Any time during the session | Rest of the trading day |
This mechanism, specific to stocks listed on regulated US exchanges like the NYSE, should not be confused with the foreign exchange market.
To place this mechanism among other protective devices, see also the article on CFD margin close-out at 50%, which describes a different mechanism specific to leveraged accounts. As explained in the article dedicated to the Forex circuit breaker, no equivalent mechanism exists on the currency side, since that market operates in a decentralized way, with no central exchange able to impose a general trading halt.
Other market incidents illustrate how a technical malfunction, distinct from a MWCB, can also paralyze transactions within minutes: this is the case of the Knight Capital software glitch, which cost 460 million dollars in 45 minutes without any circuit breaker being triggered.
Frequently asked questions about the market-wide circuit breaker
Does the market-wide circuit breaker apply to all stock exchanges worldwide?
No, the MWCB described here is specific to the US stock market and rests on NYSE Rule 7.12. It applies to stocks listed on regulated US exchanges, and its precise operation, with its three thresholds and pause durations, is only documented for this market.
Can Level 1 trigger more than once in the same day?
No, the NYSE specifies that only one Level 1 trigger and one Level 2 trigger are possible per trading day. If the index recovers and then falls back below the same 7% threshold later in the session, this does not cause a second Level 1 halt.
What happens if the 20% level is reached late in the day?
Level 3, set at 20%, can be triggered at any time during the session, unlike Levels 1 and 2, which are limited to the 9:30 a.m. to 3:25 p.m. window. Once it is reached, trading halts for the rest of the day, with no reopening before the next session.
Are options markets affected by this halt?
Yes, the NYSE states that a MWCB trigger on the stock market also halts the NYSE Arca Options and NYSE American Options markets. Any trade executed after the trigger moment on these linked markets is nullified.