How to Read Rule 10b5-1 Plan Signatures in Form 4 Filings

The single largest source of editorial misreads on insider trading data is the assumption that every CEO sale is a discretionary view on the company. It usually is not. Roughly two-thirds of large open-market sales by named executive officers at S&P 500 companies execute under Rule 10b5-1 plans — SEC-blessed pre-scheduled trading programs that explicitly insulate the trade from the executive's then-current view. Learning to recognize the data signatures of plan-driven trades is the difference between reading Form 4 filings as signal and reading them as noise.

This guide walks through the four data signatures that distinguish 10b5-1 plan execution from discretionary selling, the SEC rule structure behind those signatures, and how to use the 13F Insight insider data to spot them in practice.

Signature 1: Constant daily share count

The cleanest signature of a 10b5-1 plan is a constant share count repeated across consecutive trading days. When a plan specifies "sell 2,500 shares per trading day starting May 1," the broker executes 2,500 shares each day, regardless of price. Across a four- or five-day window, the daily disposition number is identical to the share.

You can see this signature directly in CrowdStrike CEO George Kurtz's May 2026 Form 4 cadence: 2,500 shares on May 5, 2,500 shares on May 6, 2,500 shares on May 7, 2,500 shares on May 8. The intraday prints move with the tape, but the daily total does not change. Compare that to Apple Chairman Arthur Levinson's May 6 2026 transaction — 250,000 shares in a single day, no consecutive-day pattern. The first is plan-driven; the second is more likely a single-block disposition (which may still be plan-driven, but at a single-execution level).

The exception worth knowing: some plans specify dollar-targeted rather than share-targeted execution. Those produce daily share counts that drift slightly as price moves — the lot size is recalculated each morning to hit a fixed dollar value. The shape is still recognizable as a cadence, just with small numeric drift.

Signature 2: Many small intraday prints per filing

10b5-1 plan brokers execute via algorithmic order routing — typically VWAP-style execution that slices the daily target into dozens of small child orders across the session. A single Form 4 covering a plan day routinely shows 15 to 30 individual prints at different intraday prices. Kurtz's May 8 filing shows 27 separate price levels between $493.70 and $527.98 for a single trading day.

Discretionary insider sales typically execute via a single broker fill or a small number of large block tickets. If the Form 4 shows 1 to 3 prints at one or two price levels per day, the trade was likely discretionary or blocked through a single broker. If the Form 4 shows 15+ prints across a wide intraday range, an algorithm was running.

Signature 3: Repetition across multiple consecutive trading days

A single block sale on a single day is ambiguous. A repeated pattern across multiple consecutive trading days is unambiguous — only a plan or a multi-day VWAP order produces that shape.

The data tell on Morningstar founder Joe Mansueto's May 2026 cadence is clean: 7,250 shares on May 1, 7,250 shares on May 4, 7,250 shares on May 5, 7,250 shares on May 6, 7,250 shares on May 7. Five separate filings, same daily lot size, sequential calendar dates. This is the data shape of a plan adopted in a prior open trading window and executing automatically through the current open window.

Signature 4: Adoption date footnote in the Form 4

Form 4 filings can include explicit footnotes flagging Rule 10b5-1 plan adoption. The 2023 SEC amendments to Rule 10b5-1 strengthened these disclosure requirements — new plans require a 90-day cooling-off period before first execution, and Form 4s should affirmatively flag the plan adoption date.

Where the footnote is present, the read is settled. Where it is absent, the four data signatures above (constant daily share count, many intraday prints, multi-day repetition, post-earnings open-window timing) are the next-best evidence. In practice, the data shape is usually conclusive even without the footnote — an algorithm running for four consecutive days is structurally impossible to execute discretionarily.

How to read transaction codes

Form 4 uses a controlled vocabulary of transaction codes that signals what kind of disposition occurred. The codes you will see most often on a 10b5-1 plan day:

The most common editorial mistake on this code table is conflating F (tax withholding) with S (open-market sale) in aggregate "total sold" headlines. RSU tax withholding is forced — the company auto-sells shares to cover the withholding tax obligation when an executive's RSUs vest. Including those numbers in a discretionary-disposition total is a categorical error.

What plan signatures tell you (and don't)

The key insight from learning to spot plan signatures is the inverse of the typical "CEO sells, stock falls" framing. A plan-driven sale tells you the executive scheduled a transaction during an open trading window in the past. It does NOT tell you the executive is bearish on the company today. The Rule 10b5-1 safe harbor exists specifically to break that link.

That said, plan adoption decisions still encode some information — an executive who refreshes a plan at a higher per-tranche share count when the stock has appreciated may be choosing to maintain constant dollar-velocity, or may be accelerating disposition. Distinguishing those readings requires watching the pattern over multiple quarters, not a single Form 4.

When plan signatures break down

The signatures fail in two situations worth knowing. First, when an insider terminates a plan early — for example, after a material restatement or activist campaign — the cadence simply stops. The absence of a plan-day filing is the signal, not the presence of one. Second, when an insider amends a plan during an open window to increase or decrease the per-day share count, the cadence shifts to a new constant. Watch for share-count step-changes between quarterly windows.

Using the 13F Insight platform

Every Form 4 we ingest is queryable on the per-insider profile pages. Aggregating across an insider's full transaction history makes the plan signatures obvious — the constant daily share counts cluster, the post-earnings cadence anchors to fiscal quarters, and any deviation from the pattern stands out. Start with the high-volume executives whose plans run for years (George Kurtz at CrowdStrike, Joe Mansueto at Morningstar, Arthur Levinson at Apple) and the pattern signatures jump out of the raw filing data.

For broader market-wide reads, the insights aggregate feed surfaces the most material insider transactions across the platform.