SEC Form 4 Explained: How to Read Insider Transactions

Company insiders cannot quietly buy or sell their own stock. Every time an officer, director or large shareholder changes their position, the change has to show up on EDGAR within days, on a form called Form 4. This guide explains who has to file, what the form contains, how to read the transaction codes, and how to pull the data programmatically.

What is Form 4?

Form 4 is the "Statement of Changes in Beneficial Ownership" required under Section 16(a) of the Securities Exchange Act of 1934. It reports changes in the holdings of a public company's equity securities by its insiders.

Section 16 defines an insider as:

• Every officer and director of the company.
• Any person or group that beneficially owns more than 10% of a class of the company's registered equity securities.

Insiders first disclose their starting position on Form 3 when they take on the role. After that, most changes in their holdings are reported on Form 4. Form 5 is an annual catch-all for a small number of transactions that were eligible for deferred reporting, such as certain gifts or small acquisitions under Rule 16a-13.

When is Form 4 due?

A Form 4 is generally due within two business days after the transaction that triggers the filing. This two day window has applied since the Sarbanes-Oxley Act of 2002 took effect; before that, insiders had until the tenth day of the following month.

The two tables on a Form 4

Every Form 4 is organized into two tables:

For each line, the filer reports the transaction date, the amount of securities involved, the price (if any), whether the transaction increased or decreased the position, the number of shares owned after the transaction, and whether the shares are held directly (D) or indirectly (I), for example through a trust or an LLC.

Form 4 transaction codes

The single letter in the transaction code column is the fastest way to understand what happened. The most common codes are:

A P or an S usually reflects a discretionary decision by the insider. An A, F or M is often mechanical, tied to vesting schedules, option exercises or payroll tax withholding rather than a fresh investment decision. Reading the code before the dollar amount avoids mistaking routine vesting activity for a deliberate buy or sell.

Rule 10b5-1 trading plans

Insiders often trade under a Rule 10b5-1 plan, a written plan adopted when the insider is not in possession of material nonpublic information, which sets out in advance when and how shares will be bought or sold. Since 2023, Form 4 includes a checkbox indicating whether a reported transaction was made under a Rule 10b5-1 plan, along with the date the plan was adopted. This lets you separate prearranged, scheduled transactions from trades made at the insider's discretion in real time.

What Form 4 does not tell you

Form 4 is fast and detailed, but it has real limits:

1. It only covers Section 16 insiders. Rank and file employees selling shares from an employee stock purchase plan are not covered.
2. It does not explain motive. A sale can be for diversification, taxes, a divorce settlement or estate planning just as easily as a view on the company.
3. It covers one company at a time per filer relationship. An insider at several companies files a separate Form 4 for each one.
4. Derivative positions can be complex. Options, restricted stock units and other derivatives require reading Table II alongside Table I to understand the full position.

Working with Form 4 data in code

SecFeed parses every Form 3, 4 and 5 filing into structured rows, including the transaction code, price, share counts, ownership type and the Rule 10b5-1 flag. To find large open market purchases across every company:

curl "https://secfeedapi.com/v1/insider-trading?code=P&minValue=100000&size=10" \
  -H "Authorization: Bearer YOUR_API_KEY"

Each row includes the filer, the issuer, the transaction details and the ownership type:

{
  "owner": "JANE SMITH",
  "issuer": "EXAMPLE CAPITAL MANAGEMENT LLC",
  "ticker": "EXCP",
  "code": "P",
  "transactionDate": "2026-10-05",
  "shares": 5000,
  "price": 42.17,
  "sharesOwnedAfter": 128400,
  "ownershipType": "D",
  "isRule10b51": false
}

To follow one specific insider or company over time, query by ticker, CIK or owner name. In Python:

from secfeed import Client

sf = Client("YOUR_API_KEY")
rows = sf.insider_trades(ticker="NVDA", code="S")
for r in rows:
    print(r["owner"], r["code"], r["shares"], r["transactionDate"])

The same endpoint covers Forms 3 and 5 as well, so you can see an insider's starting position alongside every later change. See the full parameter list at the insider trading endpoint.

Frequently asked questions

Who has to file a Form 4?

Officers, directors and beneficial owners of more than 10% of a public company's registered equity securities must file a Form 4 whenever their ownership changes, within two business days of the transaction.

Is Form 4 the same as insider trading?

No. Form 4 reports lawful changes in ownership that insiders are required to disclose. Illegal insider trading involves trading on material nonpublic information, which is a separate legal question investigated and enforced by the SEC, not something the form itself determines.

Why do so many Form 4 filings show code F?

Code F marks shares withheld by the company to cover tax withholding when restricted stock or similar awards vest. It is an administrative transaction, not a discretionary sale, and it often appears right after a code A or code M line.

Where can I see Form 4 filings for free?

Form 4 filings are public and free to view on EDGAR through SEC.gov, either through company search or a CIK based URL. Structured data services like SecFeed add parsing, filtering and history on top of the same public filings.

How do I know if a trade was prearranged?

Check the Rule 10b5-1 plan checkbox and adoption date on the filing. If a transaction is marked as made under a 10b5-1 plan, it was scheduled in advance under a written plan rather than decided on the day of the trade.