Short answer: the dates most Louisiana small-business owners need on the calendar are quarterly estimated taxes (mid-January, April, June and September), March 15 for S-corp and partnership returns, April 15 for individual and C-corp returns, and — the one people miss — May 15 for the Louisiana state individual return, which is a month after the federal deadline. Below is the full rhythm. Dates shift to the next business day when they fall on a weekend or holiday, so confirm the exact day each year.
The 2026 deadline rhythm
- Jan 15 — Q4 2025 estimated tax payment (self-employed & owners).
- Jan 31 — W-2s and 1099-NECs due to recipients and to the IRS/SSA.
- March 15 — S-corporation (1120-S) and partnership (1065) returns, or file an extension.
- April 15 — Individual (1040), C-corp (1120), and Q1 estimated tax. Sole props report on Schedule C with the 1040.
- May 15 — Louisiana individual income tax return (state deadline, after the federal one).
- June 15 — Q2 estimated tax.
- Sept 15 — Q3 estimated tax; extended S-corp & partnership returns.
- Oct 15 — Extended individual returns.
Exact dates move to the next business day on weekends/holidays — verify each year (this post is updated annually).
The two that trip people up
March 15, not April. If you own an S-corp or partnership, your business return is due a full month before your personal one. Owners who only think “April” file late.
Louisiana’s May 15. The state individual deadline is later than federal — handy, but it’s easy to forget the state return entirely once the April federal one is done.
Extensions ≠ more time to pay
An extension gives you more time to file, not to pay. You still need to estimate and pay what you owe by the original deadline, or penalties and interest start. This is why year-round tax planning matters — so the money’s already set aside before the deadline arrives.
The fix for deadline stress: a running tax estimate. We keep one current all year, so nothing on this list ever sneaks up on you.