The first time I read a Form 4 footnote instead of just the headline number, it permanently changed how I look at insider selling. The filing was one of those CEO-dumps-a-fortune stories that make the rounds every so often, and buried at the bottom of the form was a single line noting the sale was executed under a trading plan adopted the better part of a year earlier. Whatever that CEO knew on the day the shares hit the tape, the decision to sell was made long before, by a version of him who arguably knew far less. Reading the sale as a fresh opinion about the stock was simply wrong, and most of the commentary around it did exactly that.
This matters more than it might seem, because a large majority of insider selling at big US companies runs through these prearranged plans. They are called Rule 10b5-1 plans, after the SEC rule that created them in 2000, and if you follow insider filings without filtering for them, you are mostly reacting to noise that was scheduled months in advance.
What a 10b5-1 plan actually is
The mechanics are straightforward. Insider trading law says you cannot trade while aware of material nonpublic information, but executives are paid mostly in stock and have the same dull reasons to sell as anyone else, taxes, diversification, a house, tuition. The complication is that a senior executive is arguably never fully clean of nonpublic information. Rule 10b5-1 resolves this with an affirmative defense. Set up a written plan at a moment when you are not aware of anything material, hand your broker binding instructions, a fixed schedule, a price formula, specific amounts, and let it trade on autopilot. If the trades later land near bad news, you can point at the plan and show the decision predates the knowledge.
That is the honest use case, and for most insiders most of the time it works as intended. A CFO selling the same number of shares on the first trading day of every month for two years is managing personal finances, and treating each of those sales as a view on next quarter is a category error.
The loopholes were real, though. For years there was no mandatory waiting period between adopting a plan and the first trade, so an insider could set one up and start selling within days. Cancelling a plan does not count as a trade, so a scheduled sale could be quietly killed when the insider expected good news, and nothing would ever show up in a filing. You could even run several overlapping plans and terminate whichever ones stopped suiting you. Researchers who studied plan trades found they performed better than routine diversification selling should, and that sales beginning soon after plan adoption had a habit of preceding price declines.
What the 2023 amendments changed
The SEC tightened all of this with amendments that took effect in 2023, and the changes are worth knowing even if you never plan to be an insider. The headline change is the cooling-off period. Directors and officers now have to wait before the first trade under a new or modified plan, specifically the later of 90 days after adoption or two business days after the company files the quarterly or annual report covering the quarter in which the plan was adopted, capped at 120 days. Insiders who are not directors or officers get a 30 day cooling-off. Companies themselves got no mandatory cooling-off for their own buyback plans, which the SEC left for another day.
A few other pieces matter for reading filings. Modifying a plan in any way that changes the amount, price, or timing of trades counts as cancelling it and adopting a new one, which restarts the cooling-off clock. Overlapping plans are mostly banned, and insiders are limited to one single-trade plan in any 12 month period, which closed the trick of stacking plans and killing the inconvenient ones. Directors and officers must certify in writing that they are unaware of material nonpublic information and are adopting the plan in good faith, and the good faith requirement now applies across the whole life of the plan rather than only on day one. Companies also have to disclose in their quarterly reports when directors and officers adopt or terminate plans, so cancellations, which used to be invisible, now leave a paper trail, though with a lag.
How to spot a plan trade on a Form 4
Since the amendments, this part is mercifully easy. Form 4 carries a checkbox near the top indicating the transaction was made under a 10b5-1 plan, and the filer has to give the date the plan was adopted. Before the checkbox existed, plan sales were flagged, if at all, in a voluntary footnote, usually a line stating that the shares were sold pursuant to a Rule 10b5-1 trading plan adopted on some earlier date. Plenty of filers still write the footnote as well, and on older filings the footnote is all you get, so it pays to read them regardless.
While you are in the form, the transaction codes do a lot of work too. Code S is an open market sale and code P is an open market purchase, and those two are the only ones that can carry a real opinion. Code F is shares withheld to cover taxes on vesting equity, which is mechanical almost by definition. Code M is an option exercise, and an M immediately followed by an S is very often a same day exercise and sale of options approaching expiry, another mechanical pattern. Code G is a gift. Strip out the F, M, and G lines, then strip out the S lines with the plan checkbox ticked, and the pile of filings that deserves attention gets dramatically smaller.
The plan adoption date is the field I rarely see anyone use, and it is quietly the most interesting one. A sale under a plan adopted well over a year ago, executing in even slices, is about as informative as a payroll deduction. A large sale under a plan adopted just past the minimum cooling-off window is technically also a plan sale, but the insider chose to lock that trade in fairly recently, and the timing of plan adoption is itself a discretionary act. I do not treat those two the same way.
The filter that falls out of all this
Here is roughly how I triage insider activity, in order.
- Check the 10b5-1 checkbox and the footnotes first. A plan trade with an old adoption date and a regular cadence gets discounted to near zero.
- Strip the mechanical codes. F lines, G lines, and M plus S pairs on expiring options are personal finance plumbing and carry no view on the stock.
- For plan trades, look at the adoption date. A recent adoption followed quickly by heavy selling earns a second look, and so does a plan that was modified, since modifications restart the clock and show up in the company's quarterly disclosures.
- Flag discretionary off-plan sales, meaning code S with no plan indication, and size them against the insider's remaining holdings. Trimming a sliver to cover taxes is routine, while unloading a large share of everything they own is worth understanding.
- Weight clusters heavily. One officer selling off-plan is a maybe. Several officers selling off-plan within a few weeks of each other, at a company where insiders historically hold, is the pattern that has actually rewarded research time.
- Treat open market buys, code P, as the loudest line on any form. Insiders have endless reasons to sell and roughly one reason to spend their own cash buying.
Two caveats so the filter does not harden into a religion. Plans are not perfectly information free, because the insider still chooses when to adopt one, and terminations, while now disclosed, arrive in the next quarterly report rather than in real time, so a selling plan quietly cancelled ahead of good news remains hard to catch. And an off-plan sale justifies attention without being an automatic short thesis, since divorces, tax bills, and estate planning generate discretionary sales that mean nothing, which is exactly why the cluster test and the size test matter more than any single filing.
The takeaway fits in a sentence. Before reacting to any insider sale, open the actual Form 4, find the checkbox and the footnotes, and ask whether a human decided to sell this week or a plan decided months ago, because those two events should never move your thinking by the same amount.