Business tax deadlines: when each return and payment is due

Most federal business returns are due on the 15th day of a month that depends on the entity. Partnerships and S corporations file by the 15th day of the third month after the tax year ends. C corporations file by the 15th day of the fourth month. Sole proprietors report business income on their personal return, which is due on the same day as a C corporation's for a calendar year.

When a due date lands on a Saturday, Sunday, or legal holiday, it moves to the next business day. The dates below already reflect that for tax year 2026.

These dates assume a calendar-year business, which is most small and midsize companies. The returns are filed in 2027.

A business can ask for six more months to file with Form 7004. Individuals use Form 4868. The request has to be filed by the original due date. It gives you time to finish the paperwork. It does not give you time to pay, and interest runs on any tax that was due on the original date.

That is why a business that expects to owe tax should estimate the amount and pay it with the extension request. A partnership or S corporation normally owes no income tax itself, because the owners report the income, but it can still owe penalties for filing late.

A calendar-year C corporation files by April 15. A corporation with a fiscal year uses the 15th day of the fourth month after its own year-end, and the Form 1120 instructions carry a special rule for fiscal years ending in June, so check them if that applies to you.

A C corporation also pays estimated tax during the year if it expects to owe $500 or more. The installments are due on the 15th day of the fourth, sixth, ninth, and twelfth months of the tax year, which is April 15, June 15, September 15, and December 15 for a calendar year.

Both are due March 15 for a calendar year, a month earlier than a C corporation. The reason is practical. The owners need their Schedule K-1 to finish their own returns, so the business return has to come first.

Many owners find out in March that they need an extension to finish the K-1s, then file the owner returns on extension too. That is normal. The cost of missing the date is not: the penalty for filing a partnership or S corporation return late is charged per owner per month, for up to twelve months, and the amount is adjusted every year. A five-owner company can pay a large penalty for a return that owes no tax.

Owners of sole proprietorships, partnerships, and S corporations pay income tax on business profit through their own personal estimated payments. For a calendar year, the installments for tax year 2026 were due April 15, June 15, and September 15, 2026, and the last is due January 15, 2027.

The usual way to stay out of trouble is to pay at least as much as last year's tax in four equal installments, or 90 percent of this year's tax, whichever is smaller. The IRS has special rules for higher earners, so confirm the safe harbor with your preparer. An owner with a lumpy year can instead pay based on income earned so far, using the annualized income method on Form 2210, which usually means smaller payments early in the year.

These come up on a different calendar and are easy to forget while the income tax dates get the attention.

States have their own calendars, and they differ. Delaware, for example, asks corporations for an annual report and franchise tax by March 1, and Delaware LLCs owe a flat annual tax by June 1. Other states tie annual reports to the anniversary of formation or to the tax year-end. Sales tax and state payroll returns follow the schedule assigned to your account. Put your own states on the same calendar as the federal dates.

File as soon as you can. Penalties for late filing and late payment grow each month, and the late filing penalty is usually the larger one. For a C corporation or an individual it is 5 percent of the unpaid tax for each month or part of a month, up to 25 percent. The late payment penalty is 0.5 percent a month on the unpaid tax. Partnership and S corporation returns carry the per-owner penalty described above.

If the business has a clean compliance record for the last three years, ask the IRS about first-time penalty abatement. It is a standing administrative waiver, and it is often granted when the request is made promptly and the missed dates are explained plainly.

Enter the due dates for every return and payment the business owes, including the extended dates, with a reminder four weeks before each. Add a step to the monthly close that checks whether the information needed for the next filing is in the books. When the return is a matter of sending finished books to a preparer, the deadline stops being stressful.