A Form 4 is filed when someone covered by insider reporting rules has a change in what they hold. It is short, structured and, read carelessly, deeply misleading. Almost every mistake people make with it comes from ignoring one of four things: the second table, the transaction code, the two dates, or the holdings column.
There are two tables, not one
The first table covers ordinary securities — common stock, in most cases. The second covers derivative securities: options, restricted stock units, warrants, convertible instruments.
A single filing routinely has rows in both. An insider who exercises options and sells the resulting shares produces at least two rows across two tables describing one decision. If you read only the first table, you see a sale of shares and no idea where they came from.
Every row has a code, and the code is the meaning
The code is one or two letters and it says what kind of change happened. A purchase on the open market, an award from the company, an exercise of a derivative, shares withheld to cover tax on vesting, a gift — these are different events that all move the share count.
Adding them together produces a number that describes nothing. The two that get conflated most often are an award and a purchase: both increase holdings, one costs the insider money and the other does not.
There are two dates, and they are not the same
Each row states the date of the transaction. The filing itself has a date of submission. A Form 4 is normally due within two business days of the transaction, so the gap is small but it is real, and it is the difference between what happened and what was known.
Every insider record on this site shows both dates and the number of days between them, because a table with one date invites the reader to treat the older fact as today's news.
The holdings column is the useful one
The quantity on a row tells you the size of one change. The holdings figure tells you where the person stands afterwards. A sale of 10,000 shares means something different from a person who holds 12,000 than from one who holds 4,000,000, and only the holdings column distinguishes them.
Read the holdings figure as of the last row of the filing, not the first: rows within a single Form 4 are sequential.
What this site does and does not do with it
Each row keeps its own code, its own two dates and its own holdings figure. Where we group rows into categories, the category is labelled as derived and the underlying code stays visible. We do not score, rank or interpret the behaviour of any insider, and a filing with a large number in it is not treated as more significant than one with a small number.