Key deadlines for C corporation taxes you don't want to miss

If you leave your car in a paid parking space but don’t feed the meter, you’re probably looking at a ticket—or even a tow—by the end of the day. The same can be said for C corporations and taxes. To avoid significant penalties, these business entities must make quarterly tax payments and then file an income tax return to settle any remaining balance.

Unlike limited liability companies (LLCs) and sole proprietorships, C corps are treated as separate tax entities. This means they’re subject to stricter payment and filing requirements, making business tax deadlines even more important for several reasons, including:

• Avoiding expensive fines and interest charges
• Reducing the chances of an IRS audit
• Upholding trust with investors, lenders, and partners
• Managing company cash flow
• Preventing severe legal consequences, such as rescinded business licenses

Although business tax returns may feel like a mountainous task, we’re here to help. This guide breaks down the key C corp tax due dates, so you can avoid the fines and frustration and keep your business running smoothly.

A C corp’s payroll tax due dates generally depend on the employer’s IRS deposit schedule. For calendar year filers, key federal payroll tax deadlines include:

Payroll tax deposits

• Monthly depositors: 15^th of the month following payroll
• Semi-weekly depositors: Wednesday or Friday of the following week, depending on payroll date

Quarterly payroll tax withholding returns – Form 941

• Q1: April 30, 2026
• Q2: July 31, 2026
• Q3: November 2, 2026
• Q4: January 31, 2027

Annual tax forms

• Federal unemployment tax return (Form 940): January 31, 2027
• Federal unemployment tax return extended due date: February 10, 2027
• Form W-2 to employees: January 31, 2027
• W-2/W-3 to Social Security Administration (SSA): January 31, 2027
• Form 1099-NEC (non-employee compensation) to independent contractors: January 31, 2027

If the last day of a C corp’s fiscal year isn’t December 31, it can apply to the IRS to follow fiscal year reporting instead of the standard calendar year. If approved, the company’s deadlines shift:

• Federal taxes must be filed by the 15^th day of the fourth month after the company’s tax year-end.
• Quarterly estimated taxes must be paid on the 15^th day of the fourth, sixth, ninth, and twelfth months of the fiscal year.

For example, if your C corporation’s fiscal year ends on May 31, file Form 1120 by September 15, and make quarterly estimated tax payments by September 15, November 15, February 15, and May 15 of the following year.

When you need more time to file your C corp’s taxes, the IRS allows your business to apply for an extension. Submitting Form 7004 by your original tax deadline will provide you with an automatic six-month extension.

However, it’s critical to understand this extension is only for filing your corporation income tax return—you still must pay the IRS on time. If your corporation’s tax year ends December 31, this means:

• Tax payment is due April 15, 2026
• Extended tax filing deadline is October 15, 2026

The United States operates on a pay-as-you-go tax system, meaning companies typically pay taxes as they earn business income, rather than waiting until the end of the year.

Many self-employed taxpayers, including sole proprietors, S corp shareholders, and C corp owners, are required to make quarterly estimated tax payments based on their expected taxable income for the year.

C corps must make estimated payments if they anticipate owing $500 or more in federal income tax for the year. The IRS enforces these quarterly payments for many reasons, namely:

• Ensuring cash flow for the government
• Preventing underpayment penalties and interest charges
• Helping small businesses avoid expensive end-of-year surprises
• Cover various tax liabilities, including Medicare and Social Security

Missing just one deadline can get expensive quickly. Here are some of the substantial penalties the IRS can impose if a C corp misses a tax due date:

• Failure-to-file penalty: A C corp can be charged 5% of the unpaid tax for every month or part of a month the return is late, up to 25%.
• Failure-to-pay penalty: C corps that owe taxes face an additional penalty of 0.5% of the unpaid tax for every month or part of a month it goes unpaid, up to 25%.
• Penalty interest charges: The IRS will charge interest on both the unpaid tax and the accrued penalties, calculated daily from the due date.

On top of paying considerable fines, companies that continuously miss tax deadlines can also attract the attention of the IRS, increasing their chances of a lengthy audit.

If you have questions or concerns about meeting the deadlines, a CPA or tax professional can help you understand tax laws, bookkeeping, and getting the most tax savings from your filed tax return.