LUDPVolatility Trading Pause (Limit Up-Limit Down)
LUDP is the code you will see most often on a fast-moving small cap. It marks a Limit Up-Limit Down (LULD) volatility pause: the National Best Bid or Offer has moved to the edge of the stock's price band and stayed there, so the exchange stops trading briefly to let liquidity reset. It is a mechanical, automatic pause — not a judgment about the company.
What triggers it
- The stock quotes at the upper or lower LULD price band and remains there without moving back inside the band within the prescribed window.
- Price bands are calculated from a rolling reference price and vary by the stock's price tier and the time of day.
- Bands are widened during the opening and closing periods, which is why the same percentage move halts a stock mid-morning but not late in the session.
How long it lasts
Five minutes is the standard pause length. The exchange can extend it if the reopening auction cannot find a price inside the bands, so extended LULD pauses do occur on illiquid names.
How it resumes
The primary listing exchange reopens the security with an auction. Orders build during the pause, and the resume print is often the highest-volume trade of the session.
What it means for a day trader
LUDP is a momentum signal, not a warning. It means the move was fast enough to break the band, which is why halt-and-resume strategies are built around it.
The reopening auction is where slippage lives. The resume price can gap well away from the pre-halt print, so the pre-halt range is a poor proxy for your fill.
Repeated LUDP halts in one session — halt laddering — are common on low-float runners and are the most-studied pattern in halt backtesting.
Related halt codes
Track LUDP halts as they happen
Halt Strategy monitors live NASDAQ and NYSE halts, replays the setup around each event, and backtests outcomes segmented by halt code — so LUDP events are never averaged in with everything else.
Primary sources
Halt Strategy is research software, not investment advice, and does not execute trades. Halt procedures are set by the exchanges and regulators and can change; confirm current rules against the primary sources before acting on them. Read the full disclaimer and editorial policy.