A Form 144 is the notice an officer, director or large holder files when they plan to sell stock. Stock sites flag them as red alerts, so I measured what happened after 75,654 of them: every notice filed on EDGAR from April 13, 2023 (the day electronic filing became mandatory) to October 2025, grouped into 55,992 company-and-day events, entering at the first close after the filing was public.
Short answer: no, the stock didn't drop. What a filing reliably marks is the rally before it.
| Window | Typical stock | vs S&P 500 | vs median listed stock | Beat the median stock |
|---|---|---|---|---|
| 3 months before entry | 8.44% | +3.11 pts | +8.16 pts | 67.3% |
| 1 month after | 0.34% | -1.21 pts | +0.62 pts | 53.0% |
| 3 months after | 0.92% | -3.57 pts | +1.29 pts | 53.1% |
| 6 months after | 2.11% | -6.87 pts | +1.61 pts | 52.7% |
| 1 year after | 5.07% | -14.03 pts | +2.23 pts | 52.4% |
Medians per event. The before-window covers the 81,808 events with complete prices over those three months; the after-windows use the 55,992-event panel.
Five findings
1. The benchmark decides the headline. A year after the filing, the typical stock was up 5.07%, a little ahead of the median listed stock and 14 points behind the S&P 500. Over these windows the index rose 18.37% and the median stock 2.56%, because a few very large companies carried the market.
2. The S&P gap isn't caused by the filing. I measured the same stocks one year later, when no filing was involved. They trailed the S&P 500 by 13.52 points then, against 12.29 in the real windows on the same events: a paired difference of 1.16 points, t = 0.50. The gap belongs to the kind of company whose insiders file Form 144s.
3. Insiders sell after a rise. Two in three filings came after the stock had beaten the median listed stock over the prior three months (by 8.16 points, t = 24.09). Trading windows open after earnings, restricted stock vests on schedule, and 10b5-1 plans sell at preset prices. Selling into strength says something about the seller's plans, not the next quarter.
4. No-plan sales are a bit weaker, not bearish. On the same filing dates, notices without a disclosed Rule 10b5-1 plan did 1.65 points worse over three months than notices with one (t = 5.83), and the gap survives the placebo. They still didn't trail the median listed stock.
5. Size describes the company, not intent. Sales that are large against shares outstanding happen at small companies (median value $0.75 billion for 1% or more); sales that are large in dollars happen at big companies after big gains ($26.6 billion, up 13.4 points against the median stock in the prior three months). The two measures point in opposite directions, and in no size group was the year after the filing reliably worse than the same stock a year later.
The traps I hit
- Start at the e-filing mandate. Before April 13, 2023 most Form 144s were on paper, so the earlier electronic records are a self-selected minority.
- A notice is not a trade. Some proposed sales come in smaller or never happen; the completed sale shows up later on Form 4. I measure from the notice because that's when an outsider sees it.
- Count events, not notices. Several notices from one company on one day are one event; otherwise frequent filers (Ginkgo Bioworks filed 726, Meta 584) would dominate.
- Report two benchmarks. The S&P 500 and the median listed stock differed by about 16 points over the average year, so either one alone tells a misleading story.
- Run the placebo before calling a signal. A t-statistic of -28.70 against the S&P 500 looks decisive. It's decisive about the companies, and says nothing about the filing until the same companies are measured at another time.
- Exclude split windows and use medians. Any window crossing a recorded split is dropped, and medians keep an unrecorded corporate action from setting the result.
Check a filing yourself
With the Equibles MCP server connected to Claude or ChatGPT, a prompt like "Using Equibles, show the Form 144 notices for Datadog in the last six months, whether each disclosed a 10b5-1 plan, and how the stock did in the three months before each one" gives you the run-up check for one company.
The full study has the charts, the plan and no-plan placebo, the size and seller tables and the year-by-year breakdown: Does a Form 144 Filing Mean the Stock Will Drop? Evidence From 75,654 Insider Sale Notices.
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