When do companies file their earnings 8-Ks?
Almost never while the market is open. Of 3,994 earnings filings (July 2022 to August 2026), 3,939 (98.6%) were accepted by the SEC before 9:30 am or after 4:00 pm Eastern. And in a set of 770 we checked one by one, 745 (97%) were filed on the same day the results were announced.
Why file outside the session?
Releasing results when the market is closed gives every investor time to read them before the next trade. The press release goes out on the newswire, and the 8-K follows on EDGAR, almost always the same day. For earnings that is why the reaction shows up as an overnight gap rather than a move during the day.
Is it always the same day?
No. Most 8-K items are due within four business days of the event, and some companies use the time: of the 25 in our checked set that were not same-day, 15 were filed the next day and one four days later. Some make it a habit: one company in the checked set filed its earnings 8-K the day after the announcement nine times, so the market traded a full day on the news before it reached EDGAR.
Why do those days matter?
Because someone already knows. A study of insider trading in the gap between an event and its 8-K found that insiders' trades in that window earned abnormal returns of 42 basis points on average, and 163 basis points on open-market purchases.
The point: the date on an 8-K is not always the date the news became public. Event data has to carry the exact time each filing was accepted, and know when the news itself went out.
- Cohen, Jackson and Mitts, "The 8-K Trading Gap": Columbia Law School summary.