What Is a Circuit Breaker?
A circuit breaker is an exchange-wide mechanism that halts trading temporarily when prices fall by a predefined amount, giving markets time to calm during violent sell-offs.
What Is a Circuit Breaker?
A circuit breaker is a market-wide mechanism that pauses trading when prices fall by a predefined amount within a set period. The goal is to interrupt panic, restore orderly trading, and give participants time to reassess — not to stop prices from eventually moving.
U.S. stock market circuit breakers
The S&P 500 cash index is the reference. Three threshold levels trigger market-wide halts based on the prior day's close:
| Level | Decline from prior close | Halt duration |
|---|---|---|
| Level 1 | −7% | 15 minutes |
| Level 2 | −13% | 15 minutes |
| Level 3 | −20% | Rest of the trading day |
Key rules:
- Before 3:25 p.m. ET: Halt triggers as listed above.
- At or after 3:25 p.m. ET: Levels 1 and 2 do not halt; Level 3 still halts for the day.
- Reopening: Order book reopens with a 5-minute opening auction before continuous trading resumes.
When circuit breakers actually triggered
| Date | Event | Drop |
|---|---|---|
| Oct 27, 1997 | Asian financial crisis | −7.2% intraday (first modern halt) |
| Mar 9, 2020 | COVID-19 panic | −7% (Level 1) |
| Mar 12, 2020 | COVID + travel ban | −7% open + −9.99% close |
| Mar 16, 2020 | COVID escalation | −8.1% open (Level 1) |
In March 2020, Level 1 was triggered four times in two weeks — an unprecedented frequency.
Per-stock circuit breakers (LULD)
Beyond market-wide halts, exchanges have per-stock circuit breakers (LULD bands):
- If a stock trades outside its band for more than 15 seconds → 5-second pause.
- Reopens via auction with recalculated bands.
- Prevents runaway prints on individual names without freezing the whole market.
Other markets
| Market | Mechanism |
|---|---|
| CME futures | Daily price limits (grains, energy); some hard, others expand |
| China A-shares | Hard ±10% daily limit; ±5% for ST stocks |
| Japan (TSE) | Daily price limits by stock |
| Crypto (perpetuals) | Exchange-specific "auto-deleveraging" and funding caps; not true breakers |
| Forex | Decentralized; no formal breakers, but liquidity can vanish |
Why breakers exist
- Cool panic. A 15-minute pause lets humans (and algos) re-evaluate.
- Restore liquidity. Market makers re-enter when prices aren't falling every second.
- Prevent contagion. Slowing one market can reduce spillover to others.
- Stop algorithmic spirals. Many flash crashes are amplified by feedback loops; breaks interrupt them.
What to do during a halt
- Don't panic-cancel. Orders often re-price on reopening; knee-jerk changes are usually costly.
- Watch related markets. Bonds, futures, FX, and international indices continue trading — they signal reopening direction.
- Have a reopening plan. Know whether you want to add, reduce, or stand aside before the halt lifts.
- Expect slippage. The reopening auction can print well away from where you expected.
Bottom line
Circuit breakers are the market's brakes. They don't prevent crashes — they slow them enough for participants to think. As a trader, your job is to assume a breaker can trigger at any time, position so a halt doesn't trap you, and use the pause to make a calm reopening plan rather than a panicked one. The traders who survive violent moves are the ones who planned for them before they happened.