A trading halt is a temporary pause in trading, either in a single share or across an entire market. Circuit breakers are the automatic rules that trigger those pauses when prices move too far, too fast. They exist to give investors time to absorb information and to stop panic feeding on itself. For traders, understanding how they work helps explain some of the strangest moments on a price chart, when a market simply stops moving.
Why markets pause at all
Markets work best when buyers and sellers can find each other at sensible prices. In extreme conditions, that process can break down. A wave of selling can overwhelm buyers, prices can gap lower, and automated systems can amplify the move. A pause allows liquidity to rebuild, information to spread and orders to be reconsidered before trading resumes.
Halts are also used for more routine reasons, such as when a company is about to release price-sensitive news or when there is uncertainty about its status.
Market-wide circuit breakers in the US
In the United States, market-wide circuit breakers are based on the S&P 500’s fall from the previous day’s close. There are three levels.
- Level 1: a 7 per cent fall triggers a 15-minute pause, provided it happens before the final stretch of the session.
- Level 2: a 13 per cent fall triggers another 15-minute pause, under the same timing rule.
- Level 3: a 20 per cent fall halts trading for the rest of the day.
These levels have been triggered only rarely. The most notable recent example was March 2020, when pandemic fears caused several Level 1 halts in the space of two weeks. Our guide to the S&P 500 explains why moves in that index carry so much weight.
Single-stock halts
Individual shares have their own mechanisms. In the US, a system known as limit up-limit down prevents trades outside a band around a recent average price. If a share hits the edge of that band and does not come back within a short time, trading pauses briefly.
The London Stock Exchange uses a slightly different approach. When a share moves outside a set percentage from its last price, trading switches to a short auction, known as an automatic execution suspension period, before continuous trading resumes. The idea is the same: slow things down so the price can be found in a more orderly way.
Companies can also ask for their shares to be suspended, for instance while they finalise a major announcement. These suspensions can last much longer than automatic halts.
Futures and other markets
Futures markets have their own limits. Equity index futures can be subject to price limits, particularly overnight, which stop them moving beyond a set range until the cash market opens. Commodity futures exchanges set daily price limits on some contracts too. Forex, which has no central exchange, has no formal circuit breaker, which is one reason currency moves in a crisis can be so abrupt.
What halts mean for traders
The most important point is that you cannot trade during a halt. If you hold a position, you are stuck with it until trading resumes. Stop orders will not fill during the pause, and when trading restarts, the price may be very different from where it stopped. That is another form of the gap risk discussed in our guide to price gaps.
For spread bet and CFD traders, brokers typically suspend their own prices on a halted share, so the same applies. This is one reason guaranteed stops and careful position sizing matter when trading individual shares around big news.
There is also a behavioural lesson. Halts often occur during moments of maximum fear. When trading resumes, the first moves can be wild in either direction. Rushing to act in that chaos is rarely wise. Our guide on staying calm when the market feels chaotic is worth reading with that in mind.
Bringing it together
Trading halts and circuit breakers pause markets when prices move too far too quickly, giving time for information and liquidity to catch up. They protect the system, but they can trap individual traders in positions and lead to large gaps when trading resumes. Understanding them is part of respecting the fact that liquidity is not guaranteed.
If you want to understand how well your risk planning would cope with extreme days, our free trader assessment can show you where you stand.
