Insider buying is one of the few public signals with academic support: open-market purchases by officers, directors and 10 percent holders have historically been followed by modest positive abnormal returns, while insider sales carry almost no information [3] [4]. The evidence is strongest for purchases, for smaller companies and for clusters of buying rather than single trades. June 2026 produced several real examples, including a $50 million purchase at Summit Therapeutics (SMMT) and a scheduled buying program at 51Talk Online Education Group (COE), that show both the strength and the limits of the signal as of July 16, 2026 [1] [5] [6].
What the research says about insider buying as a signal
Two widely cited studies frame the debate. Jeng, Metrick and Zeckhauser, in a National Bureau of Economic Research working paper, found that a portfolio of insider purchases earned abnormal returns of about 40 basis points per month, with about one sixth of that gain arriving in the first five days, while a portfolio of insider sales did not earn abnormal returns [3]. Lakonishok and Lee, in a separate NBER paper, found that insiders in aggregate behave as contrarian investors, that they predict cross-sectional stock returns, that the predictive power is concentrated in smaller firms, and that purchases are more informative than sales [4].
The economic logic is simple. Executives sell for many reasons, including diversification, taxes and option expirations, so a sale says little. They buy with their own after-tax cash for one main reason: they expect the price to rise. The SEC's own investor bulletin makes the same point, noting that insiders may sell for liquidity or diversification, while many investors believe reports of insider purchases and sales can provide useful information about insiders' views of the company's prospects [2].
How the data reaches the public
Insiders must file Form 4 with the SEC within two business days of a transaction, and each line carries a transaction code. Code P marks an open-market or private purchase, code S a sale, code A a grant from the company and code M an option exercise [2]. Only code P trades are true insider buying. Grants and exercises, which DataPorium labels as stock awards and conversions in its insider transaction tables, should be excluded from any signal [1].
Recent examples of insider purchases and what happened next
| Company | Insider and role | Purchase | Close on purchase date | Close July 16, 2026 | Change |
|---|---|---|---|---|---|
| Summit Therapeutics (SMMT) | Robert W. Duggan, co-CEO, director, 10% owner | 3,810,000 shares at $13.12 on June 12 (about $50.0 million) | $14.01 | $13.76 | -1.8% |
| Nuvectis Pharma (NVCT) | Marlio Charles Mosseri, 10% owner | 50,000 shares at $18.32 on June 30 (about $916,000) | $18.39 | $18.60 | +1.1% |
| 51Talk Online Education (COE) | Jack Jiajia Huang, CEO, director, 10% owner | 216,300 shares at $19.63 to $22.82, June 8 to 15 (about $4.6 million) | $21.51 (June 8) | $16.31 | -24.2% |
Purchase details come from the Form 4 filings and DataPorium's insider transaction history; prices are DataPorium daily closes [1] [5] [6].
Summit's case is the largest. Duggan's June 12 Form 4 reports the purchase of 3,810,000 common shares at $13.12, coded P, lifting his direct holding to 573,883,879 shares [5]. DataPorium's history shows the same insider buying $5.98 million of stock in September 2025 at $17.68 to $18.07 and another purchase in October 2025 at $18.74, so the June trade continued a pattern of buying on weakness [1]. Through July 16 the stock was essentially flat at $13.76. A controlling holder adding to a very large position sends a weaker signal than a mid-level executive making a first purchase, because the marginal dollar changes little for the buyer.
Nuvectis illustrates timing risk. The stock closed at $9.75 on June 1, ran to $28.53 on June 29, then fell 36 percent in one day to $18.39 on June 30, the day of the purchase [1]. DataPorium also records the chief executive, Ron Bentsur, buying $250,000 of stock at $20.00 the same day [1]. Two insiders buying after a sharp drop is the kind of cluster the research favors, and the stock was up 1.1 percent two weeks later, but the outcome over a longer horizon remains open.
51Talk is the cautionary example. The CEO's six purchases in June were made under a Rule 10b5-1 trading plan adopted on December 25, 2025, according to the Form 4 [6]. A pre-scheduled plan removes the element of timing that gives insider buying its value; the trades happened because the calendar said so, not because the insider saw something new. The stock fell from $21.51 on June 8 to $16.31 on July 16 [1].
How investors may use insider buying without overreading it
- Weight open-market purchases (code P) only, and ignore grants, exercises and purchases under employee stock purchase plans [2].
- Prefer clusters: two or more insiders buying within a few weeks, as at Nuvectis, carry more information than one large trade by a controlling holder.
- Check whether the purchase was made under a 10b5-1 plan; the Form 4 discloses it, as 51Talk's filing does [6].
- Scale the trade to the insider's wealth and existing stake, not to the headline dollar amount.
- Expect a small edge, not a large one: 40 basis points per month in the academic sample, before costs [3].
Insider selling deserves the opposite treatment. DataPorium's records for Apple (AAPL) show the chief executive and other officers selling shares on April 2, 2026, when the stock closed at $255.92; by July 16 it closed at $333.26, up 30 percent [1]. Routine executive sales at a large company told investors nothing about the next quarter, consistent with the finding that sales are not informative [3] [4].
Open-market insider purchases carry a modest, well-documented edge, but pre-scheduled plans and top-ups by controlling holders dilute the signal to almost nothing.
Key takeaways
- Academic evidence finds about 40 basis points per month of abnormal return after insider purchases and none after sales [3].
- Summit Therapeutics' co-CEO bought about $50 million of stock at $13.12 on June 12, 2026; the shares were 1.8 percent lower on July 16 [1] [5].
- Two Nuvectis Pharma insiders bought after a 36 percent one-day drop on June 30, 2026, a cluster pattern the research favors [1].
- 51Talk's CEO purchases were made under a 10b5-1 plan and were followed by a 24 percent decline, showing why scheduled buying is not a signal [1] [6].
- Use Form 4 code P trades, check for trading plans, and treat the signal as one input among many.
Frequently asked questions
Is insider buying a reliable buy signal?
It is a modestly positive signal on average, worth roughly 40 basis points per month in the academic sample, and it is more reliable for small companies, for clusters of purchases and for first-time buyers than for controlling holders adding to large stakes.
How quickly are insider purchases made public?
Officers, directors and 10 percent holders must file Form 4 with the SEC within two business days of the transaction, and the filings appear on EDGAR and in data platforms such as DataPorium shortly after.
Does insider selling mean the stock will fall?
Usually not. Insiders sell for diversification, taxes and liquidity, and studies find no abnormal returns after insider sales. Apple insiders sold in April 2026 and the stock rose about 30 percent over the next three and a half months.
What is a 10b5-1 plan and why does it matter for insider buying?
A 10b5-1 plan is a pre-arranged trading schedule adopted when the insider has no material non-public information. Trades executed under such a plan are disclosed on Form 4 and carry little timing information, so they should be discounted as a signal.
Sources & References
- [1] DataPorium Stock Market Analytics (insider transactions and price history)
- [2] SEC Investor Bulletin: Insider Transactions and Forms 3, 4, and 5
- [3] Jeng, Metrick and Zeckhauser, The Profits to Insider Trading: A Performance-Evaluation Perspective (NBER Working Paper 6913)
- [4] Lakonishok and Lee, Are Insiders' Trades Informative? (NBER Working Paper 6656)
- [5] Summit Therapeutics Inc. Form 4 filed June 12, 2026 for Robert W. Duggan (SEC EDGAR)
- [6] 51Talk Online Education Group Form 4 filed June 18, 2026 for Jack Jiajia Huang (SEC EDGAR)
