What is Regulation SHO? Definition, Formula, and Example

Regulation SHO is the SEC rule set governing short sales in U.S. equities, requiring brokers to locate borrowable shares before shorting and to close out persistent settlement failures.

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What Is Regulation SHO?

Regulation SHO is the SEC rule set, adopted in 2005, that governs short selling in U.S. equity markets. It was written to curb naked short selling — shorting without a real ability to deliver shares — by imposing a locate requirement before a short sale and a mandatory close-out requirement when trades fail to settle. It is the regulatory backbone behind terms like failure to deliver and the FINRA threshold list.

How Regulation SHO's Rules Are Applied

Three provisions matter most to traders:

Rule 203(b) — Locate Requirement: before accepting a short sale order, a broker-dealer must borrow the security, arrange to borrow it, or have "reasonable grounds" to believe it can be borrowed for delivery. This is a locate, not a guaranteed borrow — it does not reserve shares.
Rule 203(c) — Threshold Securities: a stock is added to the Reg SHO threshold list when aggregate fails-to-deliver total at least 10,000 shares AND at least 0.5% of the issuer's total shares outstanding for five consecutive settlement days.
Rule 204 — Close-Out Requirement: a broker-dealer must close out a fail to deliver by purchasing or borrowing shares of like kind and quantity by the beginning of regular trading on the settlement day following the fail. A security that stays on the threshold list for 13 consecutive settlement days without close-out triggers a mandatory pre-borrow requirement on the broker and its customers for any further short sales.

Separately, Rule 201 imposes the Short Sale Restriction, a circuit breaker triggered when a stock falls 10% or more intraday from the prior close.

Worked Example

During January 2021, SEC settlement-fails data showed GME fails-to-deliver spiking past 1 million shares in multiple settlement cycles as short sellers scrambled to cover into a rapidly rising, hard-to-borrow name. GME and several other heavily shorted names from that period appeared on the FINRA Reg SHO threshold list, a public signal that the aggregate fail count had breached the 10,000-share/0.5%-of-float threshold for five straight sessions — meaning a meaningful share of the reported short activity in the name was not settling on time.

When Traders Use It

Squeeze hunters and short-interest analysts monitor the twice-monthly SEC aggregate fails-to-deliver data release and the daily FINRA threshold list as a proxy for settlement stress and squeeze risk on crowded shorts — a name showing persistent, rising fails alongside high short interest and a spiking borrow fee is showing structural signs that shorts are struggling to source real, deliverable shares. Compliance desks at broker-dealers use Reg SHO's locate and close-out rules as the operational gate for every short sale order that flows through their systems.

Limitations and Common Misconceptions

Regulation SHO does not ban short selling, and a "locate" is not a borrow — a broker can have reasonable grounds to believe shares are available without actually reserving them, which is how fails still occur even under the rule. The bona fide market-maker exception allows registered market makers to sell short without a prior locate to maintain liquidity, a carve-out often misunderstood as a loophole for naked shorting generally. The SEC's aggregate fails-to-deliver data is published roughly two weeks after each settlement period, making it a lagging indicator rather than a real-time squeeze signal. Finally, appearing on the threshold list does not by itself indicate manipulation — it indicates settlement friction, which can stem from operational delays as easily as from short-selling abuse.