What is an LULD Halt? Definition, Mechanism, and Example
An LULD (Limit Up / Limit Down) halt is a 5-minute trading pause triggered when a stock's price moves outside a band around its reference price, designed to prevent disorderly volatility spikes.
What Is an LULD Halt?
An LULD (Limit Up / Limit Down) halt is a 5-minute trading pause imposed when a stock's price exits a predetermined band around its 5-minute rolling reference price. The mechanism replaced the old single-stock circuit breaker in 2013 and is now the most common type of trading halt in US equities, accounting for the vast majority of intraday pauses on any given session.
How LULD Bands Work
Each security is assigned a tier that determines its band width:
- Tier 1 (S&P 500, Russell 1000, select large-cap ETFs) — ±5% during regular hours
- Tier 2 (everything else above $3) — ±10% band
- Stocks under $3 — ±20% band
- All bands double in width during the opening 15 minutes and closing 25 minutes of the session
The band is centered on a rolling 5-minute VWAP of consolidated trades. When the National Best Bid (for downside moves) or National Best Offer (for upside moves) sits outside the band for 15 consecutive seconds, the security enters a 5-minute halt. After the halt, a re-opening auction determines the resumption price.
What Happens During an LULD Halt
During the 5-minute pause:
- No orders execute — resting orders remain in the book but cannot match
- Market orders are rejected with a halt-reject error code
- Limit orders can be entered or cancelled but will not fill until the halt clears
- Options on the halted underlying are also paused
- The resumption auction produces a single clearing price, which can gap significantly from the pre-halt level
Worked Example
On a typical high-volatility session, a small-cap biotech stock trading at $10 might hit an LULD band:
1. 09:35 ET — Stock spikes to $11.50, the offer exits the ±10% band ($9.00–$11.00)
2. 09:35:15 ET — After 15 consecutive seconds outside the band, LULD halt triggers
3. 09:40 ET — Re-opening auction prints at $11.20 (within the recalculated band)
4. Trading resumes with a fresh 5-minute reference price
Stocks with high short interest and low float are disproportionately affected, as squeeze dynamics can push prices through bands rapidly.
LULD vs. Other Halt Types
- T1 halt — news pending, requested by the issuer; LULD is market-driven
- Circuit breaker — market-wide, triggered by S&P 500 index declines; LULD is single-stock
- T12 — regulatory, initiated by the exchange or SEC; LULD is automatic
Limitations and Common Misconceptions
Stops do not protect during LULD halts. A stop-loss order rests unfilled during the halt and may execute at the resumption auction price — frequently several percentage points worse than the stop level. LULD halts can repeat. A stock re-entering the band after resumption can trigger a new 5-minute halt, producing multiple consecutive pauses. Tapeboard's halt feed frequently logs the same symbol halting 5–10 times in a single session.