What Is a LULD Halt (and Why Most Traders Can't See One Coming)
Limit Up-Limit Down (LULD) is a market-wide mechanism that pauses trading in an individual stock when its price moves too far, too fast, relative to a recent reference price. The bands that trigger a pause are calculated using specific percentage rules that vary by how large the stock is (its "tier") and its current price — information that exists publicly, but isn't shown to retail traders on most standard broker screens.
Why a Calculator Instead of a Live Feed
This extension calculates the actual LULD bands from a stock's reference price and tier, then shows exactly where the current price sits relative to those bands — using the same regulatory formula the exchanges use, without needing a live market data connection.
Key Trader Pain Points and How This Extension Solves Them
| Pain Point | How the Extension Solves It |
|---|---|
| You place an order, and the stock halts mid-fill, with no warning | Shows exactly how close the current price is to triggering a halt before you submit |
| LULD band math is confusing and buried in regulatory PDFs | Calculates the actual dollar band values instantly from a reference price and tier |
| You don't know if a stock is Tier 1 or Tier 2, or what that even means for the bands | Select the tier directly and see how the percentage changes |
| Bands are different during the first/last 15 minutes of trading, and it's easy to forget | A simple toggle doubles the bands to reflect the widened-band period |
How the LULD Circuit-Breaker Proximity Alert Works
Understanding the Tier and Price Rules
| Reference Price | Tier 1 | Tier 2 |
|---|---|---|
| $3.00 and above | 5% | 10% |
| $0.75 to $3.00 | 20% | 20% |
| Below $0.75 | Lesser of 75% or $0.15 | |
During the first and last 15 minutes of regular trading hours, all of these percentages are doubled.
Step 1 — Enter the Reference Price and Select the Tier
Tier 1 covers S&P 500, Russell 1000, and select ETPs — everything else is Tier 2. Check the widened-bands box if you're within 15 minutes of the open or close.
Step 2 — Enter the Current Price
The gauge instantly shows where the current price sits between the lower and upper bands, with a plain-language risk read.
Worked Example — A Tier 1 Stock Near Its Upper Band
The setup: A Tier 1 stock has a reference price of $50.00 during normal (non-widened) hours.
The calculation: 5% band → Lower = $47.50, Upper = $52.50.
The current price: $52.30 — just $0.20 below the upper band.
The result: 0.38% away from the nearest band — Danger. A fast market order right now risks triggering a halt.
Try It: Live LULD Gauge Demo
Change any value below to see the same calculation and gauge the extension's display.
Where Traders Actually Use This
Trading the Opening 15 Minutes
During the widened-band period right at the open, a stock can move much further before halting — checking the widened bands specifically avoids underestimating how much room a stock actually has to run (or fall) before pausing.
Reacting to Breaking News Mid-Session
When a stock spikes on breaking news, a quick proximity check shows whether chasing the move risks running straight into a trading pause.
Trading Lower-Priced and Volatile Names
Stocks under $3.00 have much wider bands (20% or more) — traders in this price range use the calculator to understand just how far a stock can move before a halt actually kicks in.
A Note on Accuracy
All calculations use the standard, publicly documented LULD Plan percentage tiers, computed entirely locally in your browser — no data is sent anywhere except for an optional license check for Pro features. These percentages are set by the exchanges' LULD Plan and have been adjusted during past periods of extraordinary volatility; always verify against the current plan for anything relied upon during unusual market conditions.
Common Mistakes (and How to Avoid Them)
Fix: The bands are genuinely doubled during these windows — checking without the toggle will show bands that are too narrow for that specific time.
Fix: Tier 1 is specifically S&P 500, Russell 1000, and select ETPs — nearly everything else is Tier 2. When in doubt about a smaller or less well-known name, Tier 2 is usually correct.
Fix: The actual LULD reference price is typically an average over a preceding period, not simply the most recent trade — check your data source's specific definition before relying on the exact number.
Frequently Asked Questions
Does this connect to a live market data feed?
No. You enter the reference price and current price manually — the extension performs the regulatory calculation locally, without any live data connection.
What's the difference between Tier 1 and Tier 2?
Tier 1 covers S&P 500, Russell 1000, and select ETPs, with a tighter 5% band above $3.00. Tier 2 covers other NMS stocks, with a wider 10% band above $3.00. Both tiers share the same 20% band between $0.75 and $3.00.
Are these percentages guaranteed to be current?
They reflect the standard, publicly documented LULD Plan tiers, but exchanges have adjusted these during extraordinary volatility before. Always verify against the current LULD Plan for real trading decisions during unusual conditions.
What happens when the current price is already outside the calculated band?
The tool flags this as "OUTSIDE BAND," meaning a trading pause may already be in effect or imminent based on your inputs.
What happens after the 14-day trial?
The calculator itself keeps working fully and forever, free. Pro unlocks the ability to save a history of past checks.
