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Which Settlement Date Does the Short Interest Number on Your Screen Describe

Three Clocks Sit Behind One Short Interest Field Open a US equity on almost any broker page and you will find a line labeled short interest: a share count, often a percentage of float beside it, sometimes a days-to-cover figure. The field sits next to the last sale and the session volume, both of which update in seconds, and it quietly inherits their air of currency. It should not. The short interest field is a photograph of a settlement date that has already passed, developed and released on a calendar FINRA publishes a year in advance. On September 22, 2026, the most recent FINRA short interest figure a US screen can be showing comes from the August 31 reporting settlement date. Member firms filed it by 6:00 p.m. Eastern on September 2. FINRA released it on September 10. The next figure, capturing September 15, does not reach the public until September 24. So for twelve calendar days, the field labeled short interest has been describing the last Monday in August. That is not a ...
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A Short Sale Restriction Triggered at the Open Covers 13.0 Regular-Session Hours

The short sale price test in Regulation SHO is usually described in one line: a stock falls 10 percent and shorting gets harder. The rule is more specific than that, and two of its details decide how much the restriction actually costs a trader. One is the price the 10 percent is measured from. The other is the clock.

Rule 201, codified at 17 CFR 242.201, imposes the restriction “for the remainder of the day and the following day.” Counted in regular trading hours, that phrase produces a range rather than a number. A trigger at the opening bell covers 13.0 regular-session hours. A trigger at 3:59 p.m. covers 6.52. Identical declines, identical rule, and a coverage ratio of 1.99 to one decided entirely by when the print happened.

What follows works through the rule text, then computes the trigger levels, the hour counts and the near-miss case the rule never states. The Commission publishes the rule; the price levels, percentages, hour counts and ratios below are this article’s calculation. Rule 201 is a separate mechanism from the Regulation SHO close-out and threshold-list provisions, and nothing here is about fails to deliver.

The four operative clauses

What it covers. The definition sits at paragraph (a)(1): “The term covered security shall mean any NMS stock as defined in § 242.600(b)(65).” That is the whole universe. There is no tier, no price bucket and no market-capitalization screen.

What turns it on. Paragraph (b)(1)(i) requires a trading center to have policies and procedures reasonably designed to “Prevent the execution or display of a short sale order of a covered security at a price that is less than or equal to the current national best bid if the price of that covered security decreases by 10% or more from the covered security’s closing price as determined by the listing market for the covered security as of the end of regular trading hours on the prior day.” Two things sit inside that sentence. The benchmark is the listing market’s closing price from the prior day, not the consolidated last sale and not the session’s own opening print. And the constraint is a price test against the national best bid, not a prohibition on selling short.

How long it lasts. Paragraph (b)(1)(ii) says to “Impose the requirements of paragraph (b)(1)(i) of this section for the remainder of the day and the following day when a national best bid for the covered security is calculated and disseminated on a current and continuing basis pursuant to an effective national market system plan.” The duration is written as a condition on the bid being disseminated, not as a clock time.

Who calls it. The listing market makes the determination and must “immediately make such information available as provided in § 242.603(b).” A trader does not learn about the trigger from a price alert; the listing venue publishes it.

The 10 percent is measured from yesterday, not from today’s high

The trigger level is arithmetic on one number: 0.90 times the prior day’s official closing price. A stock that closed at $47.83 is at its trigger level at $43.047. A stock that closed at $50.00 is at its trigger level at $45.00. The rule text sets the test as a decline of “10% or more” and does not prescribe a rounding convention, so the published trigger level comes from the listing market rather than from the trader’s own division.

Three closes and their levels, to three decimals: $9.17 triggers at $8.253, $47.83 at $43.047, and $214.60 at $193.140. The third decimal is not pedantry. A $214.60 stock that falls to $193.20 is six cents short of its level and has not triggered.

Because the benchmark is fixed overnight, the size of the intraday fall and the status of the restriction can point in opposite directions. Take a $50.00 prior close. A stock that gaps up to $54.00 and then collapses 15.0 percent from that high reaches $45.90 — a fall of 8.2 percent measured from the close, and $0.90 above the trigger. A second stock that opens flat and drifts to $44.60 has fallen 10.8 percent from the close and turns the restriction on. The second stock had the smaller drawdown from its own high and the restriction it did not appear to earn.

The trigger is measured from the prior close, not from the intraday high A prior closing price of fifty dollars sets a trigger level at forty-five dollars. Path A opens at fifty-four dollars and falls fifteen percent from that high to forty-five dollars ninety cents, which is still above the trigger. Path B opens near fifty dollars and falls to forty-four dollars sixty cents, which is below the trigger and turns the restriction on. A bigger fall can leave the restriction off Both paths on one session, against a $50.00 prior close Prior close $50.00 Path A low $45.90 Trigger $45.00 Path B low $44.60 Path A opens $54.00 Path A falls 15.0% from its own high and never triggers. Path B falls 10.8% from the close and does. Source: 17 CFR 242.201(b)(1)(i). Levels and percentages are this article’s calculation.

The practical form of that is a pre-session number, not an intraday judgment. Every short candidate has exactly one trigger level for the day, it is known before the open, and it does not move when the stock rallies.

Remainder of the day, plus the following day

“The remainder of the day and the following day” is two variable pieces and one fixed piece. The first piece shrinks as the session ages. The second is a whole session regardless of what that session does.

  • Trigger at 9:30 a.m. → 6.5 hours left today + 6.5 tomorrow = 13.0 regular-session hours
  • Trigger at 10:30 a.m. → 5.5 + 6.5 = 12.0 hours
  • Trigger at 11:30 a.m. → 4.5 + 6.5 = 11.0 hours
  • Trigger at noon → 4.0 + 6.5 = 10.5 hours
  • Trigger at 3:00 p.m. → 1.0 + 6.5 = 7.5 hours
  • Trigger at 3:59 p.m. → 0.02 + 6.5 = 6.52 hours

The widest and narrowest cases differ by a factor of 1.99. The second day carries the whole weight in the late cases: a 3:59 p.m. trigger delivers 99.7 percent of its coverage on a day that has not happened yet, and on that day the stock may open higher, trade quietly and still be restricted from the first second. Regular trading hours are defined at 17 CFR 242.600(b)(88) as “the time between 9:30 a.m. and 4 p.m. Eastern Time, or such other time as is set forth in the procedures established pursuant to § 242.605(a)(3).” That definition is where the 6.5-hour block comes from and why an early-close session shortens it.

Regular-session hours covered by a Rule 201 restriction, by trigger time The restriction runs for the remainder of the trigger day plus the whole following day. Counted in regular trading hours, that is 13.0 hours when the trigger comes at 9:30 a.m., 10.5 hours at noon, and 6.5 hours when it comes at the closing bell. The same 10 percent decline, two very different sentences Regular-session hours covered, by the time the trigger is hit 6 7 8 9 10 11 12 13 9:30 a.m. 11:00 12:30 2:00 4:00 p.m. 13.0 h at 9:30 a.m. 10.5 h at noon Time the trigger is hit A 3:59 p.m. trigger still covers 6.52 hours; the range is just under two to one. Sources: 17 CFR 242.201(b)(1)(ii); hours per 17 CFR 242.600(b)(88). Counts are this article’s.

Work one case end to end. A stock closes Thursday’s prior session at $28.00, so Friday’s trigger level is $25.200. At 3:50 p.m. Friday it prints $25.10 and the listing market publishes the determination. Coverage for Friday is 10 minutes, or 0.17 hours. Coverage for Monday is the full 6.5 hours. Of the 6.67 regular-session hours the trigger buys, 97.5 percent of them fall on a session that has not opened, across a weekend, on a stock that may gap up on Monday morning and still be restricted at 9:30:01.

The calendar adds a second layer. “The following day” is the next trading day, so a Friday trigger reaches across three calendar days into Monday, and four when Monday is an exchange holiday. A position opened Friday afternoon against a triggered name is not carrying a one-session constraint.

What still prints once it is on

The clause quoted in full above blocks execution or display at a price less than or equal to the current national best bid. With a national best bid of $12.40, a short at $12.39 is blocked and a short at $12.40 is blocked, while $12.41 and $12.42 are not. Shorting continues; it simply cannot take the bid.

Two carve-outs sit in paragraph (b)(1)(iii). Subparagraph (A) permits execution of a displayed short sale order that was priced above the national best bid at the time of its initial display, which protects a resting offer when the bid later rises to meet it. Subparagraph (B) permits orders marked “short exempt.”

The cost of that constraint is not constant across the tape. Suppose the best a short can do is one cent above the bid. On a $50.00 stock that concession is 0.020 percent of price. On a $12.40 stock it is 0.081 percent. On a $2.00 stock it is 0.500 percent — twenty-five times the give-up on the $50.00 name for the same one-cent step. The rule reads identically in all three cases; what changes is what a single increment is worth relative to the position. The applicable minimum increment is set elsewhere in Regulation NMS and is assumed here only for illustration.

Where a short sale may print once the restriction is on With a national best bid of 12 dollars 40 cents, short sale orders at 12.39 and 12.40 are blocked because they are at or below the bid, while orders at 12.41 and 12.42 are allowed because they are above it. Two exceptions follow: a displayed order that was above the bid when first displayed, and an order marked short exempt. The restriction is a price test, not a ban Short sale order prices against a national best bid of $12.40 $12.42 above the bid allowed national best offer $12.41 above the bid allowed $12.40 equal to the bid blocked national best bid $12.39 below the bid blocked Two orders may still print at or below the bid (b)(1)(iii)(A) a displayed order that was above the bid when first displayed (b)(1)(iii)(B) an order the broker-dealer has marked short exempt Source: 17 CFR 242.201(b)(1)(i) and (b)(1)(iii). Prices are illustrative.

What Would Invalidate This

  • The hour counts are a floor, not a total. The rule conditions coverage on a national best bid being “calculated and disseminated on a current and continuing basis,” not on the 9:30-to-4:00 clock. The counts above deliberately exclude everything outside regular trading hours, so real coverage is at least that long.
  • The trigger level is published, not derived. The 0.90 multiplication shows where the level sits, but the listing market determines and disseminates it. Trade the published level, not the arithmetic.
  • A price test is not a liquidity forecast. Being unable to hit the bid changes the mechanics of a short entry. It does not say the stock will bounce, and the rule contains no claim about subsequent returns.
  • Exemptions are broader than the two above. Paragraph (d) enumerates further “short exempt” categories covering ownership status, arbitrage, underwriting, riskless principal and volume-weighted average price transactions. Any inference about how much short flow is actually suppressed has to account for them.
  • Early closes shorten the block. The 6.5-hour figure assumes a full session on both days. A half-day session cuts the second piece and, with it, most of a late trigger’s coverage.
  • This is not the threshold-list mechanism. Rule 201 is a price test on new short sales. The close-out and threshold-security provisions of Regulation SHO address delivery failures and operate on a different timetable.

Concrete Framework

  1. Write the trigger level next to every short candidate before the open. Multiply the prior day’s official closing price on the listing market by 0.90 and record it to three decimals. A $47.83 close gives $43.047.
  2. Measure the gap in dollars, not in percent of the day’s range. The number that matters is the distance from the current print to that fixed level. A stock down 15.0 percent from its own high can still be $0.90 above it.
  3. Time-stamp the trigger and compute coverage immediately. Hours remaining today plus 6.5 for tomorrow.
  4. Check the calendar before assuming one extra session. A Friday or pre-holiday trigger extends the constraint across the break, and an early-close session shortens the second block.
  5. Re-price short entries above the bid, and expect to wait. Orders at or below the national best bid will not display or execute. Passive offers become the working method; taking liquidity on the bid stops being available.
  6. Do not treat the exemptions as available to you. Assume the plain price test applies unless the broker states otherwise.
  7. Confirm status from the listing market’s published data. The determination is disseminated under § 242.603(b). Infer it from a chart only when the feed is unavailable, and record which source the decision used.

This article reads published rule text. It is not investment advice and recommends no security or strategy. Trigger levels, hour counts, percentages and ratios are this article’s calculations; rules are amended, so re-check them against the current text of 17 CFR 242.201 before use.

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