Business Central posts to the work date, not the calendar date. Knowing the difference stops a whole class of posting errors.
The date shown at the top left of the role centre (click the date to change it) is your work date. New documents and journal lines default to it. It is per session, per user, and it is what lets finance post last month's invoices in the first week of this month without typing the date on every line, and what lets you prepare next week's orders dated next week.
Two rules: check it before a posting session (it is the usual reason for "the posting date is not in the allowed range", tip 20), and remember it resets to today when you sign in again. %workdate in filters refers to it; %today does not. In date fields, w enters the work date and t enters today (tip 10).
