Insider Trading (Form 4): What It Tells You About a Company

When a CEO sells $50 million worth of their own company’s stock, it makes headlines. When they quietly buy $2 million worth on the open market, most investors never notice. Both of those transactions are recorded on the same SEC form — Form 4 — and learning how to read it is one of the most practical skills a retail investor can develop.

Form 4 filings are public, timely, and specific. They tell you exactly who bought or sold, how many shares, at what price, and when. Unlike 13F filings, which arrive up to 45 days after a quarter ends, Form 4 filings must be submitted within two business days of the transaction. That speed makes insider trading data one of the most actionable public datasets available to individual investors.

In this guide, we’ll break down everything you need to know: what Form 4 is, who files it, what the transaction codes mean, and — most importantly — how to distinguish routine activity from meaningful signals.

What Is SEC Form 4?

Form 4 is a disclosure document filed with the U.S. Securities and Exchange Commission (SEC). It reports changes in ownership of a company’s securities by insiders — people who have a direct relationship with the company and access to non-public information.

The legal basis is Section 16(a) of the Securities Exchange Act of 1934, which requires insiders to report transactions within two business days. The goal is transparency: the SEC wants the public to know when people with inside knowledge are buying or selling.

Each filing includes:

• The reporting person (the insider)
• The issuer (the company)
• The transaction date and type
• The number of shares transacted
• The price per share
• The shares owned after the transaction
• Whether the securities are held directly or indirectly (e.g., through a trust or LLC)

Who Files Form 4?

Three categories of people are required to file:

1. Officers — CEOs, CFOs, CTOs, COOs, and other executive officers as defined by the company
2. Directors — members of the board of directors
3. 10% beneficial owners — any person or entity that owns 10% or more of a class of the company’s equity securities

A single person can fall into multiple categories. For example, a founder who serves as CEO and owns 15% of the company is an officer, a director (if on the board), and a 10% owner simultaneously.

It’s important to note that not every insider transaction is a Form 4. Initial ownership is reported on Form 3, and annual statements of changes are filed on Form 5. Form 4 specifically covers changes in ownership that happen during the year.

Understanding Transaction Codes

Every Form 4 transaction includes a single-letter code that tells you what happened. These codes are the key to interpreting insider activity. Here’s a complete guide to the most important ones:

Code	Meaning	Signal Strength	What It Tells You
P	Open-market purchase	Strong bullish	Insider used their own money to buy shares on the open market
S	Open-market sale	Context-dependent	Insider sold shares on the open market
M	Option exercise	Weak / neutral	Insider exercised stock options (often followed by an S transaction)
A	Award or grant	Neutral	Company granted shares or options as compensation
G	Gift	Neutral	Insider gave shares away (charity, family, estate planning)
F	Tax withholding	Neutral	Shares surrendered to cover tax obligations on vested equity
C	Conversion of derivative	Neutral	Converted a derivative security (e.g., convertible note) into common stock
D	Disposition to the issuer	Neutral	Returned shares to the company (e.g., forfeiture, buyback agreement)

For a deeper breakdown of every transaction code and how to avoid misreading gifts as sales, see our detailed guide: How to Read Form 4 Transaction Codes.

The most important distinction is between P (purchase) and S (sale) codes. Everything else — M, A, G, F, C, D — is typically mechanical: compensation programs, tax obligations, or estate planning. These are routine and rarely reflect the insider’s view of the company’s future.

What Signals Actually Matter

Not all insider transactions carry the same weight. Here’s how to separate signal from noise:

Open-Market Purchases (Code P) — The Strongest Signal

When an insider buys stock on the open market, they’re spending their own money at market prices, just like you would. They’re not exercising options or receiving grants. They’re making a voluntary decision to put more of their personal wealth into the company.

Academic research consistently shows that insider purchases outperform the market on average. The reason is intuitive: insiders know their business better than anyone, and they tend to buy when they believe the stock is undervalued.

Strongest purchase signals:

• Large purchases relative to the insider’s existing holdings
• Multiple insiders buying around the same time (cluster buying)
• Purchases during or after a stock decline
• C-suite executives buying (CEO, CFO) rather than lower-ranking officers

Open-Market Sales (Code S) — Context Is Everything

Insider selling is much harder to interpret than buying. People sell for many reasons that have nothing to do with the company’s prospects: diversification, buying a house, funding a divorce, paying taxes, or simply realizing gains after years of appreciation.

Sales that deserve attention:

• A CEO who has never sold suddenly dumps a large block
• Multiple executives selling within a short window
• Sales that leave the insider with very few remaining shares
• Large sales ahead of known catalysts (earnings, FDA decisions)

Sales that are usually routine:

• Regular, pre-scheduled sales under a 10b5-1 plan
• Exercise-and-sell (M followed by S) — common for compensation liquidity
• Small sales as a percentage of total holdings

Option Exercises (Code M) — Usually Noise

Most option exercises are mechanical. Executives receive stock options as compensation, those options have expiration dates, and exercising them is part of normal financial planning. Watch what happens after the exercise: if they hold the shares, that’s a bullish signal. If they immediately sell (M followed by S), it’s typically just compensation realization.

Real Examples: Insider Activity on 13F Insight

Let’s look at three real insider profiles to see how these patterns play out in practice.

Michael Xie — Fortinet CTO ($5.8B Career Sells)

Michael Xie is the co-founder and CTO of Fortinet (FTNT), a cybersecurity company. His Form 4 history shows over $5.8 billion in career sell transactions. That sounds alarming at first glance — until you consider context.

Xie co-founded Fortinet in 2000. Over two decades, the stock has appreciated enormously. His ongoing sales represent gradual diversification of a massive concentrated position. He still retains a significant stake. This is a textbook example of a founder monetizing decades of compounded value, not a vote of no confidence.

George Kurtz — CrowdStrike CEO ($702M Career Sells)

George Kurtz, CEO of CrowdStrike (CRWD), has sold approximately $702 million in shares over his tenure. CrowdStrike went public in 2019 and has grown into one of the largest cybersecurity platforms globally.

Most of Kurtz’s sales follow a pattern common among growth-company CEOs: regular, periodic sales that are likely pre-programmed under a 10b5-1 plan. The consistency matters — it suggests planned diversification rather than reactive selling based on business concerns.

Laurence Fink — BlackRock CEO ($848M Career Sells)

Laurence Fink, the CEO of BlackRock (BLK), has sold approximately $848 million in career transactions. As the head of the world’s largest asset manager, his compensation is heavily equity-based.

Fink’s selling pattern is steady and long-running, which is typical for long-tenured CEOs of large-cap companies. His sales don’t coincide with unusual business events — they reflect ongoing liquidity needs and portfolio diversification, nothing more.

What these three examples share: high absolute dollar amounts that look dramatic in isolation but are routine when measured against holding periods, total stakes, and compensation structures.

How to Use Insider Data on 13F Insight: Step by Step

13F Insight aggregates Form 4 data into clean, browsable insider profiles. Here’s how to use the platform to research insider activity:

Step 1: Find an Insider Profile

Navigate to any stock page and look for the insider transactions section, or use the site search to find a specific insider by name. Each insider has a dedicated profile page showing their complete Form 4 history.

Step 2: Review Career Totals

At the top of each profile, you’ll see career summary statistics: total buy value, total sell value, number of transactions, and the companies where they’ve filed. This gives you a quick read on whether someone is a net buyer or net seller over their career.

Step 3: Scan Transaction History

The transaction table shows each Form 4 filing with the date, transaction code, number of shares, price per share, and shares owned after the transaction. Sort by date to see the most recent activity first.

Step 4: Look for Patterns, Not Individual Trades

A single sale rarely means anything. What matters is the pattern:

• Is the insider selling at a faster pace than usual?
• Are multiple insiders at the same company transacting in the same direction?
• Has a consistent buyer suddenly stopped buying?
• Are purchases happening after a meaningful price decline?

Step 5: Cross-Reference with Institutional Data

Insider activity is most powerful when combined with institutional data from 13F filings. If a CEO is buying while major hedge funds are also building positions, that convergence of signals is more meaningful than either data point alone. See our guide on How to Use 13F and Form 4 Together for a deeper look at combining these datasets.

Common Misconceptions

“All Insider Selling Is Bad”

This is the most persistent myth in investing. The reality: insiders sell for dozens of reasons that have nothing to do with the company’s fundamentals. Diversification, estate planning, philanthropy, personal expenses, tax obligations — the list is long. Many executives have 80% or more of their net worth tied up in company stock, so selling is basic financial hygiene.

What matters is the context: the size of the sale relative to their total holdings, whether it’s part of a pre-arranged plan, and whether multiple insiders are selling simultaneously.

“Executives Sell Because They Think the Stock Will Drop”

Some do, but most don’t. The average insider sells to manage concentration risk. A CEO whose company stock has tripled over five years may sell regularly simply to maintain a diversified portfolio. 10b5-1 plans — pre-scheduled selling programs — exist specifically so executives can sell without being accused of trading on inside information.

The exception: sudden, large, unplanned sales by multiple insiders around the same time. That pattern deserves scrutiny.

“Insider Buying Always Means the Stock Will Go Up”

While insider purchases have a statistically positive track record, they’re not a guarantee. Insiders can be wrong about their own company. They can buy because they believe in a turnaround that never materializes. Use insider buying as one input among many — not as a standalone buy signal.

“Form 4 Shows Everything an Insider Owns”

Form 4 only reports changes in ownership of specific security classes. An executive might hold shares through multiple vehicles — trusts, LLCs, family partnerships — that aren’t all visible on a single Form 4. For a broader picture of beneficial ownership, especially for large shareholders, look at 13D/G filings, which report stakes of 5% or more.

How Insider Trading Differs from 13F Data

Both Form 4 and 13F filings track stock ownership, but they serve different purposes and cover different populations:

Feature	Form 4 (Insider Trading)	13F (Institutional Holdings)
Who files	Officers, directors, 10% owners	Institutional managers with $100M+ AUM
What’s reported	Individual transactions	Full portfolio snapshot (long positions)
Filing deadline	2 business days after transaction	45 days after quarter end
Frequency	Per transaction	Quarterly
Signal type	Intent (personal capital decisions)	Positioning (portfolio allocation)

The two datasets are complementary. Form 4 tells you what company insiders are doing with their own shares. 13F filings tell you what professional money managers are doing with their portfolios. When both point in the same direction for a given stock, the combined signal is stronger than either one alone. For more on reading institutional filings, see What Is a 13F Filing?

Frequently Asked Questions

Is insider trading legal?

Yes — the term “insider trading” in the context of Form 4 refers to legal transactions by corporate insiders. Insiders are allowed to buy and sell their company’s stock as long as they report it promptly and don’t trade on material non-public information. Illegal insider trading — buying or selling based on confidential information — is a separate matter and is prosecuted by the SEC.

How quickly are Form 4 filings available?

Form 4 must be filed within two business days of the transaction. Once filed with the SEC, it becomes immediately available on EDGAR and is typically picked up by data aggregators like 13F Insight within hours.

What is a 10b5-1 plan?

A 10b5-1 plan is a pre-arranged trading plan that allows insiders to buy or sell shares on a predetermined schedule. The plan is set up when the insider does not possess material non-public information. Once the plan is active, trades execute automatically regardless of what the insider knows at the time. These plans are common among executives who need to sell regularly for diversification. Form 4 filings typically note when a transaction was made under a 10b5-1 plan.

Should I follow insider buys as trade signals?

Insider purchases are a useful data point, but they work best as confirmation of a thesis you’ve already developed, not as standalone signals. An insider buying into their own company tells you they’re confident, but it doesn’t guarantee the stock will perform well. Combine insider data with institutional position changes, earnings trends, and your own analysis.

Why do some insiders sell millions of dollars of stock and still hold a large position?

Executive compensation at large companies is heavily equity-based. A CEO might receive $20 million per year in stock awards and options. Over a decade, that accumulates into hundreds of millions — or even billions — in company stock. Selling a fraction of that each year is normal portfolio management. The key metric is what percentage of their total holdings they’re selling, not the absolute dollar amount.