Short answer: on a Form 4, the transaction code is the single letter that says what kind of trade it was. Only two codes reflect an insider choosing to trade with their own money on the open market: P (purchase) and S (sale). Most of the rest are paperwork: stock awards, option exercises, tax withholding, gifts. And of the two that matter, P is far rarer and far more informative.
We counted every transaction in the Form 4 filings we processed between October 2025 and October 2026: 158,831 transactions. Here's how often each code appeared.
How often each code appears
| Code | What it means | Share of all transactions | Tells you much? |
|---|---|---|---|
| S | Open-market or private sale | 62.8% | Sometimes (see below) |
| P | Open-market or private purchase | 11.9% | Yes, the one to watch |
| F | Shares withheld to pay tax on vesting stock or an exercise | 8.5% | No |
| A | Award or grant from the company (pay) | 8.0% | No |
| M | Option exercise (or conversion of a derivative) | 6.5% | Rarely |
| G | Gift of shares (charity, family, trusts) | 1.1% | No |
| J | "Other" acquisition or disposition, explained in a footnote | 0.4% | Read the footnote |
| D | Shares returned to the company (e.g. a buyback from the insider) | 0.4% | Rarely |
| C | Conversion of a derivative, e.g. preferred into common | 0.3% | No |
| I, L, X, W | Discretionary plan trade, small acquisition, exercise of an in-the-money option, inheritance | under 0.1% each | No |
Codes K, U, V, Z and a few others exist but didn't appear in a meaningful number of filings.
The two codes that matter
P: purchase
Code P means the insider bought shares, usually on the open market, at the market price, with their own money. Nobody makes an executive do that. That's why it's the code investors watch, and it's the only kind of trade InsiderPrint counts as "insider buying."
Purchases are rare: about 1 in 8 reported transactions, against 5 in 8 for sales. When several insiders file code P in the same stock within a couple of weeks, we call it a cluster buy.
But a P on its own isn't a winning signal. We measured 16,899 insider buying events since 2020: 46% beat the S&P 500 over the next 90 days. See which kinds did better on Setup Odds.
S: sale
Code S means the insider sold. Sales are much more common and much less informative, because insiders sell for many reasons that have nothing to do with the company's outlook: paying taxes, buying a house, diversifying, or a 10b5-1 plan set up months in advance. If a Form 4 says the sale was made under a Rule 10b5-1 plan, it was scheduled ahead of time. (How 10b5-1 plans work.)
A sale gets more interesting when it's unplanned, large compared with what the insider owns, and repeated by several insiders at once.
The codes you can usually ignore
- A (award): the company paid the insider in stock. It's compensation, not a decision to invest.
- M (option exercise): the insider converted options into shares. Often followed the same day by an S or an F, which is just cashing in or covering tax.
- F (tax withholding): the company kept some shares to cover the insider's tax bill when stock vested. It looks like a sale in some data feeds, but it isn't one.
- G (gift): shares given to a charity, family member or trust. No money changes hands.
A quick way to read any Form 4
- Find Table I (common stock) and look at the code column.
- If it's P, note the price and the dollar amount, and whether other insiders bought too.
- If it's S, check for a 10b5-1 box or footnote, and how much the insider still owns afterwards.
- Anything else: usually skip it.
Or skip the forms entirely: the latest filings on InsiderPrint show only purchases and sales, already decoded. For a box-by-box walkthrough, see How to read an SEC Form 4 in 2 minutes.
Counts: transactions in SEC Form 4 filings for U.S.-listed companies processed by InsiderPrint, October 2025 to October 2026. Not investment advice.