What Is a Limit Down?

Definition and Example of Limit Down

The term limit down refers to the maximum amount that a commodity future or stock price can decrease in a single trading day. On the flip side, the term "limit up" is the maximum amount a commodity future can increase in that daily time limit.

Both terms come from the limit up-limit down rule, a marketplace rule created by the SEC to help protect futures contracts from unusual market volatility or unexpected events in U.S. equity markets. With these events, there are typically massive changes in commodity prices. The SEC aimed to stop this volatility by preventing trades that exceed the price bands established throughout that day’s trading hours for individual exchange-traded funds (ETFs) and stocks.

If there are no limits down or up, there is a chance that a futures contract’s price will surge or drop to an irrational value simply because of market panic.

Limits in either direction can lead to pricing discrepancies between the market price and the price reflected in the corresponding futures contract. When markets make major moves during a very short time period, this can cause the contract price to reach its limit down (or limit up) for a few days before making its way toward matching the market’s price again.

You’re also likely to hear the term limit down in reference to the Limit Up-Limit Down (LULD) Circuit Breaker, a type of single-stock circuit breaker. The LULD acts as a market volatility moderator by preventing those large, sudden price moves in a stock that the Limit Up-Limit Down Rule set out to prevent.

How Limit Down Works

Limit down, and the entire Limit Up-Limit Down rule, applies to any National Market Systems (NMS) stock, which includes the majority of stocks listed on an exchange. This can include nonconvertible and convertible preferred stock.

Both limits down and limits up actively prevent trades in NMS securities from occurring outside of the previously mentioned price bands. Generally, in either direction, the limit is set as a percentage of the market price of the securities at hand.

Let’s break down how the process works. If a stock’s price moves to the price band but doesn’t move back to the original price band within 15 seconds, the stock will stop trading for five minutes.

Usually, the percentages for these price bands are 5%, 10%, 20%, or whichever is less between 15 cents and 75%. How the percentage is chosen depends on the price of the stock, the time of day the change occurs, and the tier that a stock is in.

The S&P 500, the Russell 1000, and exchange-traded products are considered Tier 1 NMS stocks. Meanwhile, NMS securities, excluding rights and warrants, are Tier 2 NMS stocks.