What LULD bands are
Limit up-limit down (LULD) is the US market-wide plan that keeps a stock from trading too far, too fast. During regular hours every stock has a lower and an upper price band around a reference price, the average price of its eligible trades over the previous five minutes. Trades cannot print outside the bands.
When the best offer sits at the lower band, or the best bid at the upper band, the stock is in a limit state. If that lasts 15 seconds, the listing exchange pauses trading, normally for five minutes, and reopens it with an auction. These are the LULD halts you see on fast small caps.
The band percentages
The percentage depends on the tier and on the stock's previous closing price. It is set from that close for the whole day and does not change intraday, even if the stock runs through a price level. A stock that closed at 0.36 and trades at 3.10 still has the 0.15 band all day.
| Previous close (US dollars) | Tier 1 | Tier 2 |
|---|---|---|
| Above 3.00 | 5% | 10% |
| 0.75 to 3.00 | 20% | 20% |
| Below 0.75 | 0.15 or 75%, whichever is less | 0.15 or 75%, whichever is less |
The percentage is applied to the reference price: a Tier 2 stock above 3.00 with a reference of 5.00 has bands at 4.50 and 5.50. Leave the previous close blank and the tool picks the percentage from the reference price instead.
Which tier a stock is in
Tier 1 is every stock in the S&P 500 or the Russell 1000, plus selected ETPs. Tier 2 is every other listed stock, so almost every small-cap momentum name is Tier 2. Index membership changes over time; the tier on a past date is the membership on that date. Rights and warrants are outside the plan and have no bands. Leveraged ETPs use multiplied percentages, which this tool does not cover.
The doubled band, and how it changed in 2020
Before 24 February 2020 the plan doubled the percentages for every stock twice a day: from 09:30 to 09:45 ET, and in the last 25 minutes before the close.
Amendment 18 to the plan, effective 24 February 2020, removed the opening doubling for all stocks. The closing doubling stayed only for Tier 1 stocks and for Tier 2 stocks priced at 3.00 or less, judged by the previous close. A Tier 2 stock above 3.00 keeps the same band all day. The closing window is 15:35 to 16:00 ET on a normal day and 12:35 to 13:00 ET on a half-day.
The tool applies the rule in force on the date you pick, so a 2019 session and a 2024 session at the same time of day can give different answers.
How the tool rounds
Each band price is rounded to the nearest cent, a half cent rounding up. A lower band that would round to zero is shown as one cent. For a reference price below one cent the band keeps its sub-penny prices, since a cent is coarser than the stock itself.
What it does not do
You enter the reference price; the tool does not compute it from trades or look up a past band for a ticker. It does not model limit states or pauses. It knows the exchange calendar for 2018 through 2027, including holidays and the half-days it lists.