First off, not all acquisitions require an 8-K. That’s a different discussion on event materiality and their triggers. That advice is wisely served by securities lawyers who have a solid background in understanding the SEC rules and defining market-practice materiality. Firms like EY can advise on the intricacies of pro forma and Reg S-X. Phew.
Below is a chart of the physical 8-K requirements an acquiring issuer needs to calendar. This is what we do.
All this would follow the S-4 filing, which also has caveats to materiality as well as if shares are actually exchanged. An S-4 is only required when the equity shares of the acquirer is being used as the “currency” (i.e. exchange offer) and only then if the target company’s shares are also publicly held. S-4s are not required for cash deals or most deals with privately held targets.