"Insider trading" gets thrown around as shorthand for financial crime. Martha Stewart went to prison for it. Rajat Gupta, former Goldman Sachs board member, went to prison for it. But the term actually describes two completely different things: one illegal, one not only legal but required by law. Conflating them causes most investors to ignore one of the most reliable signals in public markets.
Part 1: The Illegal Kind
Illegal insider trading means trading on material, non-public information (MNPI). The classic scenario: a company lawyer learns a merger is happening tomorrow, buys the stock today, profits when the news goes public.
The SEC defines the offense through two foundational legal theories:
- Classical theory: corporate insiders owe a fiduciary duty to shareholders and cannot trade on information unavailable to those shareholders.
- Misappropriation theory: outsiders who receive confidential information through a relationship of trust and then trade on it are also liable (United States v. O'Hagan, 521 U.S. 642, 1997).
The penalties are severe: up to 20 years in prison and fines of up to $5 million under the Insider Trading Sanctions Act (1984) and the Insider Trading and Securities Fraud Enforcement Act (1988).
Part 2: The Legal Kind, and Why It Matters
Here's what most people don't know: corporate insiders (CEOs, CFOs, board directors, and owners of more than 10% of a company) are permitted to buy and sell shares of their own company's stock. They just have to report it.
Section 16(a) of the Securities Exchange Act of 1934 requires these insiders to disclose any purchase or sale within two business days via Form 4, filed publicly with the SEC on its EDGAR database. So we have a universe of transactions where the most informed people in the world are putting their own money on the line. We can watch them do it in near-real time.
Part 3: What the Research Says
Academic finance has studied legal insider trading disclosures for decades. The findings are consistent and striking.
Insiders beat the market.
Seyhun (1986) was among the first to document this systematically, showing that insider purchases earned statistically significant abnormal returns in the months following the trade. His follow-up work (1992) demonstrated that aggregate insider trading activity predicted broad market returns, not just individual stocks.
Lakonishok and Lee (2001), in the Review of Financial Studies, analyzed insider trading across all NYSE, AMEX, and Nasdaq firms from 1975 to 1995. They showed that purchases are far more informative than sales. Insiders sell for many reasons (diversification, liquidity, taxes) but tend to buy for one: they think the stock is going up.
11.2%
Annualized abnormal returns from insider purchases. Jeng, Metrick & Zeckhauser (2003)
Cohen, Malloy, and Pomorski (2012), in the Journal of Finance, went further by distinguishing between routine traders (insiders who trade on a predictable schedule) and opportunistic traders (those who deviate from their routine). Opportunistic purchases earned roughly 82 basis points per month (approximately 10% annualized), while routine trades showed no predictive power.
Part 4: Why Purchases Signal More Than Sales
An insider might sell their stock because they need cash for a house, because their financial advisor told them to diversify, or because their options are expiring. Sales are noisy. Purchases are different. An executive who already receives most of their compensation in company equity, choosing to add more with their own after-tax dollars, is concentrating, not diversifying. That's a meaningful signal.
This is the informational edge: insiders see revenue trends before earnings. They know whether a drug trial is progressing. They feel the competitive landscape before it shows up in public data. When they buy, they're betting on something.
Part 5: The Signal-to-Noise Problem
If all of this is public, why doesn't everyone just follow insider trades? Because raw Form 4 data is extremely noisy. There are thousands of filings per week: options exercises, gifts, estate transfers, and automatic 10b5-1 plan trades that were pre-scheduled months in advance. Without filtering, you're drowning in transactions with no predictive value.
The meaningful signal sits in a subset:
- Open-market purchases (code P): the insider went to the market and bought at the prevailing price
- Significant dollar amounts relative to known compensation
- Not a 10b5-1 pre-scheduled plan
- Senior insiders with demonstrated historical track records
Context separates signal from noise. Not all Form 4 filings are created equal. That's exactly where the edge lives.
What This Means for Retail Investors
Legal insider trading disclosures are one of the most underutilized edges available to retail investors. The data is public, the filings are timely, and decades of academic research confirm predictive value. The challenge has always been filtering, scoring, and tracking performance at scale: turning raw EDGAR data into actionable signals. That's what Verity Signals does.
References
- Seyhun, H. N. (1986). Insiders' profits, costs of trading, and market efficiency. Journal of Financial Economics, 16(2), 189–212.
- Seyhun, H. N. (1992). Why does aggregate insider trading predict future stock returns? The Quarterly Journal of Economics, 107(4), 1303–1331.
- Lakonishok, J., & Lee, I. (2001). Are insider trades informative? The Review of Financial Studies, 14(1), 79–111.
- Jeng, L. A., Metrick, A., & Zeckhauser, R. (2003). Estimating the returns to insider trading. The Review of Economics and Statistics, 85(2), 453–471.
- Cohen, L., Malloy, C., & Pomorski, L. (2012). Decoding inside information. The Journal of Finance, 67(3), 1009–1043.
- United States v. O'Hagan, 521 U.S. 642 (1997).