How to Spot a Rule 10b5-1 Plan Sale in Form 4 Filings

When a senior insider at a public company sells stock, the SEC requires them to file a Form 4 within two business days. The filing shows the transaction date, price, and share count — but it does not, on its face, tell you why the insider sold. That distinction matters more than retail investors usually realize. A discretionary sale by a CEO who has just seen disappointing internal numbers carries one signal. A pre-scheduled sale under a Rule 10b5-1 plan, executed mechanically on a calendar date set six months earlier, carries no directional signal at all. Both can show up on the same line of a press release as "CEO sells $X million in shares."

This guide covers how to tell them apart using only the public Form 4 data you can pull from our institutional signals feed or directly from SEC EDGAR. The structural fingerprints are reliable enough that you can usually answer the plan-versus-discretionary question before the explanatory footnote appears in the filing.

What Rule 10b5-1 actually does

SEC Rule 10b5-1 was adopted in 2000 to give corporate insiders a structured safe harbor against insider trading liability. The mechanism is simple: an insider adopts a written trading plan during an open trading window, specifies in advance the dates, prices, or share quantities at which trades will execute, and then steps back. The plan is then executed mechanically by a broker on the pre-specified schedule, with no input from the insider once it's running.

The protection is that any sale executed under a properly adopted 10b5-1 plan cannot, by definition, reflect material non-public information at the time of execution — because the insider's discretionary involvement ended at plan adoption. In 2023, the SEC tightened the rules: 90-day cooling-off period for directors and officers between adoption and first sale, certification requirements, and explicit disclosure on Form 4 when a sale is plan-driven.

The three structural signatures

Three diagnostic patterns appear consistently in 10b5-1 plan executions and are absent or weak in discretionary sales.

1. Lot-size fragmentation

A 10b5-1 plan typically gives the executing broker a daily share cap and a price-improvement instruction. The broker fills that cap from multiple inventory pools at multiple price points throughout the trading day. The result on Form 4 is a single transaction date with five, ten, or twenty separate line items at distinct lot sizes. The April 2026 sales by Arista Networks CEO Jayshree Ullal are a textbook example: 20 separate transactions across three consecutive trading days, with lot sizes ranging from 219 shares to 36,685 shares.

A discretionary sale, by contrast, clusters. A CEO who decides today to sell $50 million typically gives the broker one large block order or two; the resulting Form 4 has one or two large round-number lots at one or two close prices. The cleaner the cluster, the more discretionary it looks.

2. Price-band distribution

Plan executions clear at multiple distinct limit prices on each trading day. The price improvement algorithm matches the daily share cap against the order book at whatever clearing levels the market provides — so you see executions at $171.77, $172.46, $173.12, $173.94, $175.35, $176.18, $177.87, $178.88, and $180.00 across the same filing. The recent Joe Mansueto sales on MORN showed exactly this signature: 12 distinct price points across three trading days.

Discretionary sales typically clear at one or two reference prices because the insider gives the broker a target price or a market order, not an open limit. If you see a Form 4 with three or fewer execution prices across all line items, the trade is more likely to be discretionary.

3. Cadence consistency over multiple filings

The third signature is harder to see in a single Form 4 but emerges across a quarter of filings: 10b5-1 plans tend to refresh on consistent schedules. Annual or semi-annual plan adoption dates create predictable sale clusters at the same time each year. If you pull an insider's complete Form 4 trading history and see the same approximate sale volume in the same approximate weeks each year, that's a plan running on a yearly refresh.

Discretionary sales are irregular by construction. If they happened predictably they would already be plan-driven. A long-time founder who has never sold and suddenly sells $200M is far more diagnostic than the same founder selling $200M as the latest tranche of a multi-year program.

The four common false readings

Retail investors who haven't internalized these signatures often read three categories of transaction as bearish when they are not:

• Tax withholding at RSU vest (Code F): When an RSU grant vests, the company typically withholds enough shares to cover the recipient's income tax liability. These F-code transactions are forced, not directional. The CEO did not choose to sell shares — they chose to accept compensation, and the IRS demanded a portion in cash.
• Option exercise paired with sale (Codes M + S): When an insider exercises options, the standard form ("cashless exercise") sells enough shares simultaneously to cover the strike price and tax liability. The remaining shares the insider keeps. The S-code line on the same date as the M-code line is mechanically connected, not a directional sale.
• Charitable gift (Code G): Gifts to a foundation or family trust appear on Form 4 but do not put downward price pressure on the stock — the donee usually holds. Reading these as a sale is a category error.
• "Owns zero shares" framing on Table I only: Form 4 Table I shows non-derivative direct holdings. Dual-class shares, derivatives, and trust-held positions sit in Table II. Many founder-CEOs hold the bulk of their stake in Table II and look like they own nothing in Table I. The Mansueto family 13G/A disclosure showing 47% combined beneficial ownership is the corrective for that framing.

The cross-checks that actually matter

When you do see a Form 4 that fits the discretionary profile (clustered execution, one or two price points, irregular cadence, no plan footnote), the right next step is institutional cross-check. Pull the company's consensus institutional holders and ask whether active discretionary managers (not the BlackRock / Vanguard / State Street passive index trio) are trimming in the same window. If active institutional holders are selling alongside, the discretionary insider signal is corroborated. If active holders are buying, the insider may be reading something the institutions disagree with — and the institutions may be right.

The other useful cross-check is the Schedule 13G/A filings on the same stock. Beneficial ownership disclosures by the founder and their family entities reveal whether percentages are eroding over time. If a founder is filing Form 4 sales but their beneficial ownership percentage is holding steady year-over-year, they are tracking pace with company-level share buybacks rather than exiting. The live institutional signals feed tracks these threshold movements across the market.

Reading insider stories on 13F Insight

Every insider news article in our database surfaces these signatures explicitly. The transaction code table, lot-size distribution, price-band scatter, and 13G/A cross-check are part of the standard analytical layer rather than the dollar headline. Cases where we explicitly conclude "plan-driven" rather than "discretionary" — like the Mansueto $3.7M MORN sales and the Ullal $135M ANET sales — show the diagnostic in action.

For deeper reading, see the explainer library for related concepts: Schedule 13D versus 13G disclosure obligations, Form 4 transaction code semantics, and how beneficial ownership reporting works for control-holding founders. Cross-reference SEC's own Rule 10b5-1 plain English guide for the regulatory framework. The directional question — should I sell when an insider sells? — almost always has the same answer: only after you've established whether the insider chose to sell or was forced by the calendar.