Limit Up Limit Down

What is Limit Up Limit Down (LULD)?

Limit Up Limit Down, or LULD, is the U.S. equity market mechanism that sets dynamic upper and lower price bands for each individual NMS stock during the regular session and prevents trades outside them. When the national best quote reaches a band and that Limit State persists for 15 seconds, the primary listing exchange declares a trading pause that starts at five minutes.

LULD acts on one stock at a time. Market-wide circuit breakers use S&P 500 declines to coordinate broad-market trading halts.

How are LULD price bands calculated?

The securities information processors calculate the reference as the arithmetic mean of eligible reported trades over the prior five minutes and apply the security’s assigned parameters. In the ongoing calculation, the reference updates once the required 30-second interval and 1% movement test are satisfied.

In the worked example, the Tier 1 stock’s previous close places it in the above-$3 bucket. Before the final 25-minute period, its $25 reference and 5% parameter give a $1.25 distance. The lower band is $23.75 and the upper band is $26.25.

Tier, price bucket and product determine the parameters. During the final 25 minutes, parameters double for all Tier 1 securities and Tier 2 securities priced at or below $3. Low-price and leveraged-product provisions supply their specified adjustments.

How a Limit State leads to a LULD trading pause

An upper Limit State starts when the national best bid equals the upper band without crossing the best offer. A lower Limit State starts when the best offer equals the lower band without crossing the best bid. The processor identifies the relevant Limit State quotation.

If all Limit State quotations execute or cancel within 15 seconds, the state clears. A state that persists triggers a trading pause. The initial pause is five minutes, followed by the primary exchange’s reopening procedure. Further extensions follow its rules until the reopening conditions are met.

How trading reopens after a LULD pause

The reopening auction brings eligible orders together before continuous trading resumes; late-day pauses follow the applicable closing process. Use the official trading status, active bands and order confirmations to follow the event. Review the quantity and limit of each open order.

For options on the stock, follow the contract’s exchange status and quote alongside the underlying. Read the reopened stock price and completed volume before updating the position plan.

Limitations of Limit Up Limit Down

• LULD bands apply to individual NMS stocks during the regular session. They do not cover the broad market, which market-wide circuit breakers handle.
• The bands move with the reference price, which updates after the 30-second interval and 1% movement test. A gradual move carries a stock a long way over a session without a pause, because the bands walk with it.
• Check each stock’s band before you trade a fast move. Tier, price bucket, time of day and product adjustments set the width, so a 5% move puts one stock in a Limit State and leaves another trading.
• The reopening auction sets the next price after a pause. A stock paused at $26.25 reopens wherever the auction clears, so price orders for the auction, not the band.

Bottom line

Limit Up Limit Down keeps each NMS stock’s regular-session trades inside dynamic price bands and turns a Limit State that lasts 15 seconds into a trading pause and a reopening auction. Track the active bands and the official trading status, and review every open order’s quantity and limit before trading resumes.