Short Sale Restriction (SSR): Rule 201 Counted on 30 Large Caps

Michael Whitman · Trading since 2017, full-time since 2020 · Published 2026-09-25

Traders call it SSR, the SEC calls it a circuit breaker, and the rule text calls it paragraph (b) of Rule 201 in Regulation SHO. Whatever the label, it does one narrow thing after a steep one-day drop: it stops short sellers from selling at the bid. This page sets out the rule as written, walks a real trigger in Microsoft from January 2026 through to the minute it expired, and counts how often it switched on across 30 large US stocks since the rule took effect.

How it works

The trigger is a 10% fall from yesterday’s close. Under 17 CFR 242.201, the restriction starts when a stock’s price is down 10% or more from its closing price on the prior day, as set by the exchange where it is listed. The SEC’s staff answers on the rule add two details: the price that counts is a reported trade, not a quote, and only trades during regular trading hours, 9:30 a.m. to 4:00 p.m. Eastern, can set it off.

The restriction is a price test, not a ban. Once it is on, trading venues must stop any short sale from executing or displaying at a price at or below the current national best bid, the highest bid across all exchanges. A short seller can still sell, but only by offering above that bid and waiting for a buyer to come up and take it.

It lasts the rest of that session and all of the next one. The following day means the next trading day, and the SEC’s answers say the test applies whenever a national best bid is being published, which includes early and late trading on that day. A fresh 10% fall while the restriction is already on sets it off again, so it can roll forward day after day.

Exemptions and the rule’s history

Some orders are exempt, but not by the trader’s choice. A broker can mark certain short sales “short exempt”: one it identifies as priced above the national best bid when it is sent, a market maker offsetting odd lots, a riskless principal fill, and a handful of arbitrage, underwriting and VWAP cases. These are broker-level marks with written procedures behind them.

The dates matter for any history. The SEC adopted Rule 201 in 2010 and, after one extension, set compliance for 28 February 2011, which is where the count on this page starts. It is often called the alternative uptick rule because it applies a price test only after a drop rather than to every short sale at all times.

What changes on a restricted day

For a short seller, the marketable order disappears. A sell-short order that would have to hit the bid cannot execute there. Take a hypothetical quote of $430.00 bid and $430.05 offered: a short sale limited at $430.00 cannot fill or display, while one at $430.01 or higher can rest in the book. In a stock that is still falling, a resting offer above the bid may never be reached.

For everyone else, nothing changes. Selling shares you own is a long sale and is untouched. Buying to cover an existing short is a purchase, so it is untouched too. The price test only governs new short sales.

It is not a halt. A trading pause under limit up-limit down, or a market-wide circuit breaker, stops trading altogether for a period. Rule 201 lets every kind of order keep trading and only moves where one kind of order may execute.

A worked example

Microsoft closed at $481.63 on 28 January 2026. Ninety percent of that is $481.63 x 0.90 = $433.467, so the line sat at $433.47.

On 29 January MSFT opened at $439.99, already $41.64 or 8.65% lower, but still above the line. It then traded down to a low of $421.02, which is 12.58% below the prior close. The first reported trade at $433.47 or lower switched the restriction on for the rest of 29 January and the whole of 30 January.

The close made the day look milder than it was. MSFT finished 29 January at $433.50, 9.99% down, three cents above the line. A screen that looks only at closing changes would have missed this trigger entirely, yet short sellers still faced the price test for the whole of the next session.

30 January did not trigger again. A new trigger would have needed a trade at or below 90% of the 29 January close: $433.50 x 0.90 = $390.15. The 30 January low was $426.45 and the close $430.29, down 0.74%. The restriction therefore expired at the end of 30 January, and on 2 February short sales could hit the bid again even as MSFT kept sliding.

The original data

The sample is 30 large companies checked every day since the rule took effect. AAPL, MSFT, NVDA, AMZN, GOOGL, META, TSLA, BRK-B, JPM, V, MA, JNJ, WMT, XOM, CVX, PG, KO, PEP, HD, COST, MRK, ABBV, BAC, DIS, CSCO, INTC, NFLX, AMD, BA and NKE, from 28 February 2011 to 25 September 2026, using Yahoo Finance daily bars. A trigger day is one whose regular-session low was at or below 90% of the prior close. That gives 116,765 stock-days.

Triggers were rare: 363, or 0.31% of stock-days. That is about one in every 322. They fell on 242 different dates, and two stocks supplied almost a third of them: TSLA with 60 and AMD with 57. Procter & Gamble triggered once, and Alphabet and Costco twice each. Every trigger is listed, with its prior close, line, low, close and next session, in the trigger-day file.

Stress arrives all at once. 2020 alone produced 101 trigger days, and 16 March 2020 put 27 of the 30 stocks under the restriction on the same session. 24 August 2015 caught 16. The quietest years, 2017 and 2023, had 7 each. 2026 has 20 so far. The yearly counts include how many stock-days each year contributed.

Most triggers happened after the open, not at it. 103 of the 363 (28.4%) opened at or below the line. The other 260 crossed it during the session, as MSFT did. At the close, 172 (47.4%) were still 10% or more down; the rest had climbed back above the line. The deepest, Netflix on 20 April 2022, opened below the line, had a low 39.04% under its prior close and closed 35.12% down.

SPY triggered once. On 16 March 2020 the fund’s low of $237.36 was 11.87% below the prior close of $269.32, so the line at $242.39 was crossed. The rule covers every NMS stock, so exchange-traded funds are included.

The restricted day had no lean, only width. On the session after a trigger the median close-to-close change was +0.13%, against +0.06% across all 116,735 next sessions in the sample, and it closed higher 51.0% of the time against 51.9%. What did differ was size: the median move, up or down, was 2.66%, over three times the 0.83% of an ordinary day. The next day re-triggered 18 times.

Caveats that change the edges, not the picture. Yahoo lows can differ by a cent or two from the listing exchange’s record, and 41 of the 363 triggers had a low within 0.2% of the line, so a slightly different data source would move the count by a few. The list is 30 companies that are large today, which tilts toward names that survived and grew.

When it fails

It does not stop a fall. Nearly half of the triggers closed below the line anyway. Netflix on 20 April 2022, the deepest trigger in the sample, had the restriction in force from the first trade and still closed more than a third lower.

It is not a signal that shorts are trapped. SSR is sometimes read as bullish for the next day, on the idea that sellers are hobbled. The next-day count above, 51.0% higher against a base of 51.9%, gives that idea nothing to stand on.

It catches traders who plan from the close. MSFT on 29 January 2026 closed 9.99% down and still left a restricted day behind it. A plan to short the next morning at the bid would have met a venue that would not fill it.

It widens the gap between intent and fill. Because a short sale must sit above the bid, a stop or bracket built around a short entry can end up entered late or not at all, and on a day that moved three times its usual size, the price you finally get can be a long way from the one you planned.

Related

The short selling page covers the borrow, the fee and the uncapped risk that exist whether or not a restriction is on. The circuit breaker page explains the halts that stop trading outright, which Rule 201 does not do. And the bid price page explains the national best bid that the rule measures every restricted short sale against.

This page is educational, not financial advice. Test every idea on your own charts before risking money.