What Is a Short Tax Year? Definition & Basics for Form 1120 Filers

When Tax Year ≠ 12 Months

Most tax returns cover a full 12-month period — typically January 1 through December 31 for calendar-year filers. But the IRS sometimes requires a tax return for a shorter period. That shorter period is called a "short tax year."

A short tax year is any tax year less than 12 months. The IRS treats short-year returns differently from regular returns in subtle but important ways: due date calculation, election validity periods, and how income/deductions are annualized.

Why This Comes Up for Foreign-Owned LLCs

Foreign-owned LLCs hit short tax years in three common scenarios:

1. First year of operation. If you formed your LLC mid-year (e.g., October 15, 2025), your first tax year runs October 15 - December 31, 2025 — only 78 days. That's a short tax year.

2. Final year. If you dissolve the LLC mid-year (e.g., June 30, 2026), the final tax year runs January 1 - June 30, 2026. That's a short tax year.

3. Accounting period change. If you change from a calendar year to a fiscal year (or vice versa), the transition year is a short tax year. This is rare for foreign-owned LLCs but happens occasionally.

How a Short Year Affects Form 5472 Filing

The Form 5472 + pro forma 1120 obligation applies to short tax years the same as full tax years. If your LLC existed for 78 days in 2025, you still file Form 5472 for those 78 days. The §6038A $25,000 penalty applies if you don't.

The due date for a short-year return is based on the short year's end date. If your short year ends June 30, the return is due by the 15th day of the 4th month after — so October 15. If the foreign-owner extension applies, due dates shift accordingly.

The tax year fields on Form 1120 and Form 5472 must reflect the actual short period. On Form 1120, that's the "For calendar year [YEAR], or tax year beginning [DATE], and ending [DATE]" line at the top of page 1. Fill the beginning and ending dates with the short period.

Three Real Scenarios

Scenario A — First year: LLC formed October 15, 2025. Tax year: October 15 - December 31, 2025 (78 days). File Form 5472 + pro forma 1120 by April 15, 2026 (the standard April 15 + extensions).

Scenario B — Dissolution year: LLC formed January 2020, dissolved June 30, 2026. Final tax year: January 1 - June 30, 2026 (181 days). File the final-year Form 5472 + pro forma 1120 by October 15, 2026 (15th day of 4th month after June 30).

Scenario C — Accounting period change: LLC operated on a calendar year for years; now switches to a fiscal year ending September 30. Transition tax year: January 1 - September 30 (273 days, less than 12 months). Requires IRS approval via Form 1128 (Application to Adopt, Change, or Retain a Tax Year), filed in advance. After approval, the short year filing proceeds normally.