On March 9, 2020, the S&P 500 opened and immediately fell 7%. Within seconds, trading across every major U.S. stock exchange stopped. For 15 minutes, nobody could buy or sell a single share. It was the first market-wide circuit breaker to trip in over two decades.
Over the following two weeks, it happened three more times.
Circuit breakers are one of the most consequential — and least understood — rules in markets. Every investor who holds stocks is subject to them. Yet most people don't know the specific thresholds, how long halts last, or what happens to their orders when markets freeze.
This guide covers everything you need to know.
What Are Stock Market Circuit Breakers?
A circuit breaker is an automatic mechanism that halts trading when prices move too far, too fast. The name comes from electrical engineering: just as a circuit breaker cuts power to prevent a fire when a current surges, a market circuit breaker cuts trading to prevent a panic-driven freefall from becoming a catastrophic collapse.
The core idea is simple. During extreme volatility, markets can enter a self-reinforcing spiral: falling prices trigger stop-loss orders, which cause more selling, which pushes prices lower, which triggers more stops. Circuit breakers inject a mandatory pause that gives participants time to process information and make rational decisions rather than reacting in blind panic.
Why Circuit Breakers Were Created
The origin traces directly to Black Monday, October 19, 1987. The Dow Jones Industrial Average fell 22.6% in a single day — the largest single-day percentage drop in history. The crash was amplified by computerized program trading strategies that automatically sold when prices dropped, creating a cascade effect with no natural floor.
The Brady Commission, which investigated the crash, recommended automatic trading halts as a safeguard. The SEC and exchanges implemented the first circuit breakers in 1988.
The rules have been revised significantly since then. The current system — the one that applied during the 2020 COVID crash — was adopted in 2012, replacing an earlier version that used Dow Jones points as the threshold instead of percentages.
The Three Market-Wide Circuit Breaker Levels
Market-wide circuit breakers are triggered by declines in the S&P 500 index measured against the prior day's closing price. There are three distinct levels, each with different rules:
| Level | S&P 500 Decline | Before 3:25 PM ET | After 3:25 PM ET |
|---|---|---|---|
| Level 1 | 7% drop | 15-minute halt | Trading continues |
| Level 2 | 13% drop | 15-minute halt | Trading continues |
| Level 3 | 20% drop | Market closes for the day | Market closes for the day |
A few important rules govern how these levels interact:
Level 1 and Level 2 are each triggered only once per day. If a Level 1 halt occurs at 10:15 AM and markets resume, they won't halt again at Level 1 even if the S&P falls another 7% from the reopening price. The Level 2 halt can still trigger if the total decline from the prior close reaches 13%.
The 3:25 PM cutoff matters enormously. In the final 35 minutes of the regular session, Level 1 and Level 2 circuit breakers do not apply — halting trading so close to the close could create more disruption than it prevents. Level 3 (20% decline) is the only circuit breaker that applies in the final 35 minutes, and it closes the market for the entire remainder of the day.
All U.S. equity markets halt simultaneously. When the NYSE trips a circuit breaker, trading stops across NYSE, Nasdaq, Bats, and every other U.S. equities exchange. The halt is coordinated and universal.
What Happens During the Halt
When a circuit breaker trips:
- All incoming orders are rejected
- The current order book is frozen
- Options markets also halt
- Futures markets continue trading (CME Group has its own, different circuit breaker rules — more on that below)
- After 15 minutes, markets reopen with a brief auction to establish a new price
The March 2020 Circuit Breaker Events
The 2020 COVID crash is the best recent case study for understanding how circuit breakers actually function in practice.
| Date | Event | Circuit Breaker |
|---|---|---|
| March 9, 2020 | S&P 500 falls 7% at open on oil price war news | Level 1 — 15-min halt at 9:34 AM |
| March 12, 2020 | S&P 500 plunges 9.5% as WHO declares pandemic | Level 1 — 15-min halt at 9:31 AM |
| March 16, 2020 | S&P 500 opens down 9.7% | Level 1 — 15-min halt at 9:30 AM |
| March 18, 2020 | S&P 500 falls 7% early session | Level 1 — 15-min halt at 9:35 AM |
All four events were Level 1 halts — the market never reached a Level 2 (13%) or Level 3 (20%) halt during any single session, though the cumulative decline from peak to trough exceeded 34%. This illustrates an important point: circuit breakers don't prevent large sustained market declines. They interrupt single-day panics. They are not a backstop against bear markets.
The halts in March 2020 were generally credited with helping: when markets reopened after each 15-minute pause, selling pressure moderated compared to what computer models suggested would have happened without intervention.
Single-Stock Circuit Breakers: The LULD Bands
Market-wide circuit breakers are the dramatic headline events. But there's a second system that operates constantly, on every individual stock, every trading day: the Limit Up–Limit Down (LULD) mechanism.
Implemented by the SEC in 2013 as a permanent replacement for the "single-stock circuit breakers" introduced after the 2010 Flash Crash, LULD prevents individual stocks from trading outside a defined price band.
How LULD Bands Work
For each stock, LULD calculates a reference price (the average transaction price over the preceding five minutes) and applies percentage bands above and below it:
| Stock Type | LULD Band (Each Direction) |
|---|---|
| S&P 500 and Russell 1000 stocks, ETFs priced ≥ $3.00 | 5% |
| All other NMS stocks priced ≥ $3.00 | 10% |
| All stocks priced $0.75–$3.00 | 20% |
| All stocks priced < $0.75 | Lesser of $0.15 or 75% |
During the opening and closing (9:30–9:45 AM and 3:35–4:00 PM ET), bands are doubled to accommodate the higher volatility typical during those periods.
When a stock's price moves to the upper or lower limit:
- A 15-second pause begins
- If trading resumes within the band before the 15 seconds expire, no halt occurs
- If trading cannot resume within the band, a 5-minute trading halt is triggered
Unlike market-wide circuit breakers, LULD halts apply to individual securities — other stocks continue trading normally while one stock is halted.
Why LULD Matters for Traders
LULD halts can happen to any stock, at any time, for reasons that have nothing to do with company news. They often occur in:
- Small-cap stocks with thin order books where a few large orders can move price dramatically
- Stocks with pending news (earnings, FDA decisions, M&A) where price movement triggers the band before the news is fully distributed
- ETFs during periods of extreme market stress when the underlying basket components are disrupted
If you hold a position in a stock that gets LULD-halted, you cannot exit until the halt is lifted. For active traders, this creates execution risk that stop-loss orders cannot fully mitigate.
Trading Halts: LULD vs. News-Pending Halts vs. Regulatory Halts
Not every trading halt is a circuit breaker. There are three distinct types of single-stock halts, and it's worth knowing the differences:
| Halt Type | Triggered By | Duration | Who Initiates |
|---|---|---|---|
| LULD halt | Price moves outside LULD band | 5 minutes | Exchange (automatic) |
| News-pending halt | Company requests time to disseminate material news | Variable (typically 30 min–2 hrs) | Company or exchange |
| Regulatory halt | SEC or FINRA investigation, trading irregularities | Variable (hours to days) | Regulator |
News-pending halts are the most common type most investors encounter. When a company announces earnings, a merger, or other material news, exchanges often halt trading in that stock briefly to allow the information to spread before trading resumes. These halts are typically announced in advance on the exchange's halt list and resume once the news is out.
Regulatory halts are far less common and generally more serious. The SEC can halt a stock for up to 10 trading days if it believes trading is occurring on inaccurate or misleading information. These halts are relatively rare but when they occur, they can last days or longer.
What Happens to Your Open Orders During a Halt?
This is a practical question with an important answer: it depends on the type of order and the type of halt.
During a market-wide circuit breaker halt:
- Open limit orders remain queued in the order book and are not automatically cancelled
- Stop-loss orders that haven't yet been triggered remain pending — they don't execute during the halt
- Market orders submitted just before the halt may have been partially filled or sit in the queue
- When the halt ends, a reopening auction processes the queued orders at a new price
During a single-stock LULD or news-pending halt:
- Limit orders remain in the book
- Stop orders that would have triggered at prices within the LULD band may execute at the halt's reopening price, which could be significantly different from where you placed your stop
- Market orders submitted during a halt are typically rejected immediately
The critical risk: if a stock opens substantially lower after a halt ends — say, 20% below your stop price — your stop-loss order executes at whatever the reopening price is, not at the price you intended. This is called slippage and it's why many professional traders use limit orders rather than market stop orders.
Circuit Breakers in Futures and Options Markets
Equity circuit breakers only apply to stocks. Derivatives markets have their own rules.
CME Futures (S&P 500 E-mini)
The CME Group, which operates the E-mini S&P 500 futures market, has price limits (not halts) at:
- Down 5% from prior settlement: Trading continues but only at or above the limit level ("limit down")
- Down 7%: Corresponds to the equity Level 1 circuit breaker — a 15-minute halt
- Down 13%: Corresponds to the equity Level 2 circuit breaker — a 15-minute halt
- Down 20%: Trading is halted for the day
Critically, futures don't halt overnight. The 7% and 13% levels only correspond to the equity halts during regular trading hours (9:30 AM – 4:15 PM ET). Outside those hours, futures continue trading but the price limits still apply. This is why, in March 2020, futures were already "limit down" before the equity open — and why the circuit breakers tripped almost immediately when stocks opened.
Options Markets
Options exchanges halt in coordination with the underlying equity halt. If AAPL stock is LULD-halted, AAPL options stop trading simultaneously. Market-wide circuit breakers halt all options markets. Traders with options positions that need to be hedged during a halt have no mechanism to do so — another form of execution risk during volatile periods.
How to Prepare for Circuit Breaker Events
You cannot trade around a circuit breaker after it trips. The only useful preparation is before the fact.
Position Sizing and Concentration
The simplest protection is not being over-concentrated in a position that could be halted. A position that represents 30% of your portfolio can do serious damage if it's halted and resumes 15% lower. A position representing 3% is a bad day, not a crisis.
Know Your High-Risk Periods
Circuit breakers are far more likely in specific circumstances:
- Open-market reactions to overnight news (geopolitical events, major economic data released pre-market)
- Earnings gaps for volatile individual stocks (biotech, small-cap tech)
- Macro shock events (pandemic announcements, Fed surprise decisions, major credit events)
These aren't the moments to be overweight a fragile position. Use the screener to filter for high-volatility stocks before earnings — stocks with high ATR and thin float are more likely to hit LULD bands.
Use Real-Time Alerts to Stay Informed
During a normal trading day, most circuit breakers give almost no advance warning. A market-wide circuit breaker trips the instant the S&P 500 crosses the 7% threshold — there's no 30-second countdown.
What you can monitor is the market's approach to dangerous levels. If the S&P 500 is already down 4-5% and showing accelerating downside, a circuit breaker becomes a realistic possibility within that session. Real-time alerts on S&P 500 percentage moves — set at -3%, -5%, and -7% from prior close — give you a heads-up as conditions deteriorate, long before any halt actually occurs.
Similarly, watching for individual stocks approaching LULD band limits (unusual intraday moves of 8-12% that could push into halt territory) via percentage-move alerts gives you the opportunity to act before execution is taken away from you.
The Bottom Line
Circuit breakers are a deliberate feature of U.S. markets, not a bug. They exist because unchecked panic selling has historically created crashes far deeper than the underlying facts warranted — and because giving participants a 15-minute pause to think has, on the evidence, reduced damage during genuine crises.
For most long-term investors, circuit breakers are background knowledge: useful to understand but unlikely to affect any single holding decision. For active traders, they're an operational reality that affects order execution, position risk, and how to structure entries and exits around high-volatility events.
The key takeaways:
- Three market-wide levels: 7% (15-min halt), 13% (15-min halt), 20% (closes market). Level 1/2 don't apply in the final 35 minutes.
- LULD bands protect individual stocks from flash crashes — they fire every day, on any stock, automatically.
- Open orders survive halts but may execute at very different prices when trading resumes.
- Futures and options have their own halt rules that create additional complexity during market-wide events.
- Preparation matters more than reaction — position sizing and real-time alerts are the practical tools available to traders.
Ready to monitor market conditions in real-time? Try StockAlarm Pro free for 7 days — real-time alerts across 10,000+ stocks, crypto, forex, and futures. No credit card required.
Related Articles
- Stock Market Trading Hours: Pre-Market, Regular Session, and After-Hours
- How to Set Stock Price Alerts: Complete Guide
- Average True Range (ATR): How to Measure Volatility
- Day Trading Alerts: How to Set Up Your Real-Time Alert System
This article is for educational purposes only and does not constitute investment advice. All investing involves risk.
