When Is a Business Tax Return Due, and What If You Missed It?

The business tax return deadline depends on how your company is taxed, and for 2025 every one of them, extended dates included, is now behind us. If you searched "last date to file corporate tax return 2025," here are the dates, what a late return costs, and the order to fix it in.

When was the 2025 business tax return due?

For calendar-year businesses, the IRS due dates for 2025 returns were:

The usual date for partnerships and S corps is the 15th day of the third month, March 15, but it fell on a Sunday in 2026. Form 7004 gives an automatic six-month extension to file, not to pay. Not sure which return applies to you? See which tax form your LLC or corporation files.

Late filing penalty for Forms 1065 and 1120-S

Partnership and S corp returns usually show no tax, so many owners assume being late costs nothing. It doesn't work that way: the Form 1065 late filing penalty and the Form 1120-S late filing penalty are charged per owner. For returns due in 2026, the IRS charges $255 for each month or part of a month the return is late, times the number of partners or shareholders, for up to 12 months. That's up to $3,060 per owner.

Example: a two-owner LLC that filed no extension and files its 2025 Form 1065 in early December 2026 is in its ninth month: 2 × $255 × 9 = $4,590. Each Schedule K-1 not given to an owner on time can add another $340.

Form 1120 late filing penalty for C corporations

A C corporation pays its own tax, so its penalty is based on what it owes: 5% of the unpaid tax for each month or part of a month, up to 25%. If the return is more than 60 days late, the minimum is the smaller of $525 or the tax due. Unpaid tax also picks up a late-payment penalty of 0.5% a month (up to 25%) plus interest.

How to reduce a late business tax return penalty

1. File now. Every new month adds to the per-owner penalty until you hit 12.
2. Pay what you can if the return shows tax, to slow the penalties and interest.
3. Ask for First Time Abate. It covers late-filing penalties on business returns, including 1065s and 1120-Ss, if the same return was filed on time for the prior three years with no penalties. You can call the number on the notice or send a letter or Form 843. The IRS says it is moving this relief to automatic, starting summer 2026.
4. Otherwise, show reasonable cause. Wait for the penalty notice and then send your explanation; don't attach it to the return.

Behind on the books, too? Our Form 1065 guide and Form 1120-S guide list what each return needs. Late on your personal return as well? Read filing taxes late.

NJ corp tax and New York business return deadlines

• New Jersey: for 2025 returns, the NJ corp tax due date was April 15, 2026 for the CBT-100S and May 15, 2026 for the CBT-100: the 15th day of the month after the federal due month. Late filing costs 5% a month of the tax due, up to 25%, and a $100-a-month penalty may also apply. Every corporation owes at least the minimum tax ($500 to $2,000 for a CBT-100, $375 to $1,500 for an S corp), so a "zero" return is generally not allowed.
• New York: the CT-3-S is due March 15 and the CT-3 April 15 for calendar-year filers. Late returns add 5% a month, up to 25%. A late CT-3-S can also cost $50 per shareholder a month, up to $250 per shareholder.

Business tax deadlines for 2026 returns

Don't repeat it next year. Your business tax return due date for 2026 depends on the return: Forms 1065 and 1120-S for 2026 are due March 15, 2027, and Form 1120 is due April 15, 2027. For returns due in 2027, the per-owner penalty rises to $260 a month and the Form 1120 minimum to $535.

Merchant Financial Advisory (MFA), an accounting, tax and business solutions provider in Princeton, New Jersey, prepares late business returns and handles penalty relief requests for small and mid-sized businesses in New Jersey, New York and nationwide. See our late tax return service, or book a call.