Business Tax Returns and Deadlines

Every entity form maps to one federal return and one hard deadline. The cost of missing a pass-through deadline is not a percentage of tax owed — it is a flat, per-owner, per-month penalty that runs whether or not the entity earned a dollar. Know your form and your date before the year begins.

The penalties that hurt are the pass-through ones. A late or missing Form 1065 or Form 1120-S draws a penalty of $260 per partner or shareholder per month, up to twelve months, under IRC §6698 and IRC §6699 — the figure is indexed annually, and $260 is the amount for returns required to be filed in 2027. A four-owner partnership that files five months late therefore owes $4\times 5\times \$260=\$5,200$ before anyone computes a dollar of income tax, and each late K-1 to an owner carries its own information-return penalty on top. Pass-throughs can extend six months on Form 7004, but an extension moves the filing deadline, not the tax payment deadline; tax still accrues interest from the original date.

Off a December year-end, read the rule and not the date. The calendar dates above are dynamic consequences, not fixed statutory calendar dates: pass-through returns are due the 15th day of the third month after the close of the tax year and corporate returns the 15th day of the fourth — so a June 30 year-end puts Form 1065 on September 15 and Form 1120 on October 15. A long-running carve-out that let June 30 C-corporations file a month early expires for tax years beginning after 2025, so a fiscal-year filer working from older guidance should re-derive the date instead of blindly repeating last year’s.

Employment and information returns run on a separate calendar. Payroll returns ( Form 941 quarterly, Form 940 for federal unemployment annually) and the W-2 and 1099 information returns covered in section “Paying for Work: Payroll and Information Reporting” are due January 31, independent of the income-tax return. The state layer — franchise tax, sales tax, and the state income return — carries its own deadlines, usually but not always tracking the federal date. Put every recurring date on a calendar with two weeks of buffer; the penalties above are pure deadweight, entirely avoidable, and routinely paid by businesses that simply lost track of the date.