Market Circuit Breakers: How a 7% Drop Pauses Trading

Key Takeaways

• Market circuit breakers halt all US equity trading at S&P 500 declines of 7 percent (Level 1), 13 percent (Level 2), and 20 percent (Level 3), with Level 3 closing the market for the day.
• Level 1 and 2 halts only apply before 3:25 PM ET; after that cutoff, the market keeps running even if the 7 percent threshold is breached.
• Investors often assume halts prevent crashes, but circuit breakers slow the sequence rather than stop it, all four 2020 COVID Level 1 halts still resulted in significant losses on those days.
• During a halt, S&P 500 futures on CME continue trading, which is how the broader market reprices risk before the equity reopen auction.

What It Is

The modern US market-wide circuit breaker (MWCB) regime was introduced in response to the October 1987 crash, then amended in 1998, 2010, and most significantly in 2013 after a review prompted by the 2010 Flash Crash. The rules live in exchange rulebooks, most visibly NYSE Rule 7.12 and Nasdaq Rule 4121, and apply across all US equity and options exchanges simultaneously.

The thresholds are measured against the previous trading day's closing price of the S&P 500 Index:

Level 1 : -7%   halt for 15 minutes (before 3:25 PM ET only)
Level 2 : -13%  halt for 15 minutes (before 3:25 PM ET only)
Level 3 : -20%  halt for the remainder of the day

A separate system, Limit Up-Limit Down (LULD), handles single-stock volatility pauses. Circuit breakers are index-level; LULD is name-level. Both can fire on the same day.

The Intuition

Crashes tend to feed themselves. Forced sellers, margin calls, stop orders, and risk-parity rebalancing all accelerate the same direction. In a fast market, liquidity providers widen spreads or withdraw entirely, so each successive sell order clears at a worse price, creating more forced sellers.

A short pause interrupts the feedback. It does not prevent losses. It gives firms time to calculate risk, get margin confirmations, and for natural buyers to reposition. The historical record suggests circuit breakers slow crashes rather than stop them. Black Monday 1987 lost 22.6 percent on the Dow in one session, before circuit breakers existed. In March 2020, Level 1 halts triggered on four separate trading days during the COVID selloff without a Level 3 halt ever hitting.

How It Works

The thresholds are recalculated daily by the SIP (Securities Information Processor) administrators based on the prior session's S&P 500 close. Halts are coordinated across all US equity exchanges and are announced on the consolidated tape.

Timing rules matter. Levels 1 and 2 only halt between 9:30 AM and 3:25 PM ET. Inside that 3:25 PM cutoff, any 7 percent decline halts trading for 15 minutes. Outside that cutoff, the market keeps running even if the 7 percent level is breached, because a 15-minute pause near the close would push the reopen past 4:00 PM. Level 3 (a 20 percent decline) applies at any time during the session and halts the market for the rest of the day.

When a halt fires, trading stops on every US exchange for the affected securities. Listed options trading also halts. Equity index futures (for example, S&P 500 E-mini) continue to trade on the CME, subject to their own price limits and pauses. Overnight index futures are in fact how the next session's open often sets up after a prior-day halt.

Resumption uses a reopen auction on each primary listing exchange, similar to a morning open. The first print after a halt is typically based on aggregated imbalance information rather than continuous trading.

Worked Example

The S&P 500 closes on Monday at 5,000. Tuesday morning the SIP publishes these Level prices:

Level 1 threshold = 5000 * 0.93 = 4,650
Level 2 threshold = 5000 * 0.87 = 4,350
Level 3 threshold = 5000 * 0.80 = 4,000

Tuesday the market opens down. By 10:45 AM the index hits 4,650. Trading halts across all US equity venues for 15 minutes. Equity index futures on CME continue trading, subject to their own 7 percent daily limit (which may itself be locked). At 11:00 AM, the reopen auctions run and continuous trading resumes.

If selling continues and the index reaches 4,350 at, say, 1:30 PM, another 15-minute halt is triggered. There is no second Level 1 halt; the system skips straight to Level 2. If the decline reaches 4,000 at any time, Level 3 fires and trading closes for the day regardless of the clock.

This scenario is close to what happened on March 9, 12, 16, and 18 of 2020. Each of those days triggered a Level 1 halt at the open or shortly after. The market reopened each time and finished the session without escalating to Level 2 or 3.

Common Mistakes

1. Confusing market-wide circuit breakers with LULD halts. MWCB is an index-level pause triggered by the S&P 500. LULD is a single-stock pause based on each name's rolling five-minute reference price. Both exist, both can fire, and the mechanics are entirely different.

2. Thinking halts close the underlying market. A Level 1 or Level 2 halt is a pause, not a close. Trading resumes after 15 minutes. Only a Level 3 halt closes the session. Equity index futures keep trading on CME, with their own limits.

3. Assuming futures pause with cash equities. Futures halts exist but follow CME rules, not exchange circuit breakers. S&P 500 futures have their own limit-up and limit-down bands, typically 7 percent overnight and separate daytime levels. During an equity halt, cash is frozen but futures often keep printing, which is how dealers reprice risk.

4. Believing circuit breakers prevent crashes. They do not. 1987 happened before circuit breakers existed, and the 2010 Flash Crash happened under the pre-2013 regime. The goal is to slow the sequence, not to guarantee a floor.

5. Forgetting other markets do not halt. FX markets trade continuously and do not halt for equity circuit breakers. US Treasuries, overseas stock markets, and crypto continue to reprice, which means news between a Level 1 halt and the reopen can push the reopen auction to a very different level than the halt price.

Frequently Asked Questions

Q: What are market circuit breakers in simple terms? Circuit breakers are automatic market-wide pauses triggered when the S&P 500 drops enough in a single session. A 7 percent drop triggers a 15-minute halt, 13 percent triggers another, and 20 percent closes the market for the rest of the day.

Q: How do market circuit breakers affect investment decisions? They create a brief window during which you cannot buy or sell US equities. Index futures continue to trade, so the reopen price can be materially different from the halt price. Having open orders near the halt level means they may fill at the reopen auction, not at your intended price.

Q: What is a real-world example of market circuit breakers? March 9, 2020: the S&P 500 dropped 7 percent at the open, triggering a Level 1 halt at 9:33 AM. Trading resumed at 9:48 AM. The same pattern repeated on March 12, 16, and 18 during the COVID selloff. No Level 2 or Level 3 halt was reached on any of those days.

Q: How can investors prepare for market circuit breakers effectively? Keep cash or liquid positions sized appropriately so a 15-minute halt does not trap you in an illiquid position at a critical moment. Monitor S&P 500 futures during any halt to estimate where the reopen auction will price.

Q: How are market circuit breakers different from LULD trading halts? Circuit breakers are index-level pauses for the entire market triggered by S&P 500 moves. LULD halts are single-stock pauses triggered by that individual stock's price moving outside its own rolling price band. Both can occur on the same day.

Sources

1. New York Stock Exchange. "Market-Wide Circuit Breakers FAQ." https://www.nyse.com/publicdocs/nyse/NYSE_MWCB_FAQ.pdf
2. U.S. Securities and Exchange Commission, Investor.gov. "Stock Market Circuit Breakers." https://www.investor.gov/introduction-investing/investing-basics/glossary/stock-market-circuit-breakers
3. UTP Plan. "SIP Market-Wide Circuit Breaker Overview." https://www.utpplan.com/DOC/MWCB_SIP_Overview.pdf
4. New York Stock Exchange. "Report of the Market-Wide Circuit Breaker Working Group." https://www.nyse.com/publicdocs/nyse/markets/nyse/Report_of_the_Market-Wide_Circuit_Breaker_Working_Group.pdf

Disclaimer

This article is educational content only and is not financial advice. Nothing here is a recommendation to buy, sell, or hold any security. Consult a licensed advisor before making investment decisions.