Which Form 4 code means an insider bought stock?

Code P — an open-market or private purchase at the prevailing market price. It is the only code that represents an insider choosing to acquire shares with their own money. Codes A and M also appear as acquisitions but are a grant and an option exercise respectively.

What does transaction code M mean on a Form 4?

Code M is the exercise or conversion of a derivative security — options becoming common stock. It is a paperwork event, not a purchase, and the resulting shares are frequently sold the same day under a separate code-S line.

What is transaction code F?

Code F is the payment of an option exercise price or tax liability by delivering or withholding shares. When a stock grant vests, the company keeps some of the shares to cover the tax bill. It is automatic and carries no signal about the insider's view.

Every SEC Form 4 Transaction Code, in One Sortable Table

The SEC defines twenty transaction codes for Form 4. Four of them account for the large majority of filings, and only one — P — reliably means an insider decided to buy.

The table below has every code, the classification this site assigns it, roughly how often it turns up, and a one-line read on what it actually tells you. Filter by code, by meaning, or by a word like "tax"; sort by frequency to see which codes you will actually encounter.

Filter

Code	Classification	Frequency	What it means
P	Open-Market Purchase	Common	A decision to buy. Own money, market price.
S	Open-Market Sale	Very common	A decision to sell — unless it was scheduled under a 10b5-1 plan.
A	Grant / Award	Very common	Not a trade. Compensation the company awarded.
M	Option Exercise	Very common	Not a trade. Options becoming shares, often sold the same day.
F	Tax Withholding	Very common	Not a trade. Shares withheld to pay tax on a vesting award.
G	Gift	Common	A gift. No money, no price.
D	Disposition to Issuer	Common	Shares handed back to the company under an equity plan.
C	Conversion	Uncommon	A derivative converting to stock. Mechanical.
X	In-the-Money Exercise	Uncommon	An in- or at-the-money option being exercised.
I	Discretionary Transaction	Uncommon	A discretionary move within a benefit plan — low signal.
V	Voluntary Early Report	Rare	A marker, not a kind of trade: it means the filer reported early.
O	Out-of-the-Money Exercise	Rare	An out-of-the-money option being exercised — unusual.
J	Other	Uncommon	Other acquisition or disposition (footnote required)
K	Equity Swap	Rare	Transaction in equity swap or instrument with similar characteristics
L	Small Acquisition	Rare	Small acquisition under Rule 16a-6
U	Tender of Shares	Rare	Disposition pursuant to a tender of shares in a change of control transaction
W	Inheritance	Rare	Acquisition or disposition by will or the laws of descent and distribution
Z	Voting Trust	Rare	Deposit into or withdrawal from voting trust
E	Short Position Expired	Rare	Expiration of short derivative position
H	Long Position Expired	Rare	Expiration (or cancellation) of long derivative position with value received

Frequency bands are approximate, from how often each code appears across filings we parse. Classifications are the same ones stored on every transaction on this site.

The four you will see constantly

A — Grant or award. Shares the company handed over as compensation. Shows as an acquisition; is not a purchase. Extremely common because most senior pay is equity.

M — Option exercise. A derivative converting to stock. Often paired with a same-day S sale — the "cashless exercise". A paperwork event.

F — Tax withholding. When a grant vests, the company withholds shares to pay the tax. Shows as a disposal; is not a sale.

S — Open-market sale. A real sale — but check the 10b5-1 flag before reading anything into it, because most large sales are pre-scheduled.

The one that carries signal

P — Open-market purchase. The insider bought shares at the market price with their own money. No compensation mechanism produces a P. It is the highest-signal line on a Form 4, and it is far rarer than the acquisition codes above.

The long tail

Codes like G (gift), D (disposition to the issuer), C (conversion), X and O (in- and out-of-the-money option exercises), W (inheritance) and Z (voting trust) each show up occasionally and almost never carry a trading signal. J ("other") requires a footnote by rule — if you see a J, the explanation is in the footnotes and you have to read it.

V is not a kind of trade at all: it is a marker meaning the transaction was reported earlier than the deadline required.

The short version

Learn P, S, A, M and F and you can read most of what crosses the wire. P is buying. S is selling, with an asterisk. The rest is compensation machinery that changes an insider's share count without anybody deciding to trade.