Electing Large Partnerships: File Form 1065-B calendar year return. Furnish Sch. K-1 to each partner. For automatic 6-month extension File Form 7004. Calendar Add to Calendar Add to Timely Calendar Add to Google Add to Outlook Add to Apple Calendar Add to other calendar Export to XML When: March 15, 2018 all-day 2018-03-15T00:00:00-07:00 2018-03-16T00:00:00-07:00 ← Corporations: Deposit the fourth installment of your 2018 estimated tax.Deposit payroll tax for payments on Mar 10-13 if the semiweekly deposit rule applies. →