Periodic Returns. Quarterly (Form 941N) by last day of month following end of quarter. Monthly (Form 501 N) by the 15th of the following month if more than $500 withheld for either of the first two months of a quarter.
Annual Reconciliation Returns. Form W-3N due March 15.
Timely Filing. Returns and reports considered timely filed if
postmarked by their due date. If the due date for filing any return falls on a
Saturday, Sunday, or a legal holiday, the due date is the next business day.