Business Tax Deadline, the April Wednesday

A C corporation on a calendar year files Form 1120 on the 15th day of the fourth month. In 2026 that day is Wednesday 15 April. It does not move. The March Monday belongs to partnerships and S corporations.

People who have only ever filed a personal return see 15 April and assume every company uses it. A C corporation happens to land there in 2026. An S corporation does not. The letter in the file is the only way to know which row you are on.

IRS Publication 509 is the table for the weekend rule. A due day that lands on a weekend moves to the next business day.

An owner who also has a company may owe estimates in April, June, September, and the January after the year. Those are the owner's dates. The company's April filing is the return. Putting both jobs on one sticky note is how a payment gets missed while the return goes out, or the reverse.

IRS Publication 505 is where the estimate math lives. The safe-harbor arithmetic stays in that publication and is not copied onto this site.

We keep the two calendars on one page in the file and on two lines in the conversation. The Wednesday can hold a return. It should not be asked to hold every other obligation by memory.

The months through December have to be closed, or the return is a draft with a date on it. A C corporation that has not tied the year will feel the Wednesday as a threat. Closed months turn it back into a filing day.

The books for a C corporation are kept here, and Form 1120 is prepared from the year those books already closed. We do not represent you before the IRS. If the Wednesday has already passed, file next. The filing charge and the payment charge are different, and this page does not restate either table.