Circuit Breakers: Trading Halts and Market-Wide Safeguards
Circuit breakers are automatic trading halts triggered by large market declines. After the 1987 Black Monday crash (22.6% drop in one day), regulators implemented market-wide circuit breakers. In March 2020, the S&P 500 triggered a Level 1 circuit breaker four times in two weeks as COVID fears crashed markets.
There are two types of circuit breakers: market-wide and single-stock. Market-wide circuit breakers are triggered by S&P 500 declines from the previous day's close. Level 1 (7% decline) halts all trading for 15 minutes if triggered before 3:25 PM ET. Level 2 (13% decline) also triggers a 15-minute halt if triggered before 3:25 PM. Level 3 (20% decline) halts trading for the remainder of the day. The levels reset at the start of each calendar quarter. The 15-minute halts give traders time to assess information, place orders, and avoid panic-driven selling. After the halt, trading resumes with an auction to establish an opening price.
Single-stock circuit breakers are known as Limit Up/Limit Down (LULD). Introduced in 2012 after the 2010 Flash Crash, LULD prevents trades in individual stocks from occurring outside updated price bands. If a stock's price moves more than a certain percentage (ranging from 5% for liquid large-cap stocks to 20%+ for small caps) in a 5-minute period, trading halts for 5 minutes (or longer for larger moves). The bands are recalculated every 30 seconds based on the stock's average price over the preceding 5 minutes. LULD prevents the kind of extreme price dislocations seen in the Flash Crash, when some stocks traded at $0.01 despite being worth $40.
Real-world example: In March 2020, the COVID-19 pandemic triggered four Level 1 circuit breakers in nine trading days: March 9 (7.6% decline), March 12 (9.5% decline), March 16 (12% decline — this triggered a Level 1 at the open and since it occurred before 9:35 AM, the halt was only 15 minutes), and March 18 (5.2% decline — not enough for a circuit breaker but still severe). The S&P 500 fell 34% from its peak to trough. Each circuit breaker pause allowed the market to stabilize temporarily, though selling resumed after each halt. Without circuit breakers, the selling could have been even more disorderly. The halts gave market participants time to reassess and prevented a cascading crash.
How to Trade During Circuit Breakers
During a market-wide halt, all stocks, ETFs, options, and futures stop trading on all US exchanges. You cannot enter, modify, or cancel orders — they are queued and processed when trading resumes. After the 15-minute halt, trading resumes with a "reopening auction" that establishes a single opening price based on accumulated buy and sell interest. Be prepared for volatile opens — prices can gap significantly from where they halted. Do not place market orders immediately after a halt; the spread may be wide. Use limit orders to control execution price. Circuit breakers are not trading signals — they do not predict whether the market will go up or down after the halt. In 2020, the market continued to fall after circuit breakers. In 2024, the market rallied after a halt. Focus on your long-term plan, not the short-term technical event.
FAQs
How often have circuit breakers been triggered?
Market-wide circuit breakers have been triggered only six times in history. The first was in 1997 when the Dow fell 7.2% (the trigger was then based on the Dow, not the S&P 500). In March 2020, the new S&P 500-based circuit breakers triggered four times. Since then, they have not been triggered (as of 2026). Single-stock LULD halts are much more common — thousands occur each year, especially for small-cap stocks, SPACs, and meme stocks. In 2021, GameStop triggered over 100 LULD halts in a single month during the short squeeze. Most single-stock halts last 5 minutes and are a normal part of market functioning.
Do circuit breakers prevent crashes?
Circuit breakers do not prevent crashes — they slow them down. By pausing trading, they give participants time to process information, assess valuations, and place rational orders rather than panic-sell into a void. The theory is that 15-minute halts prevent the cascading feedback loop of panic selling. Evidence suggests circuit breakers are modestly effective — they reduce volatility in the immediate aftermath of the halt, but the market often continues in the same direction after trading resumes. Circuit breakers are better understood as "speed bumps" than as crash prevention mechanisms. They make markets more orderly but do not change the underlying supply and demand.
What happens to my open orders during a circuit breaker?
During a market-wide circuit breaker, all orders are queued — they are not canceled, modified, or executed. When trading resumes after the 15-minute halt, the exchange conducts a reopening auction. Your market orders will execute at the auction price (which could be significantly different from the price when trading halted). Your limit orders enter the order book at the reopening. If you want to change or cancel an order during a halt, you must wait until trading resumes. During a single-stock LULD halt, orders for that stock are queued but orders for other stocks continue to trade normally.