Important tax deadlines for S corporation business owners

If you ever travel somewhere that requires multiple layovers, missing the first flight can cause a landslide of consequences. One delay can cost you hundreds—if not thousands—of dollars as you claw your way to your destination.

Missing your S corporation tax deadline can have the same catastrophic effect. This is because S corps, like limited liability companies (LLCs), sole proprietorships, and partnerships, are pass-through entities. For S corps, this means:

• All business profits, losses, tax deductions, and tax credits are reported on the business owners’ personal income tax returns, and the business doesn’t pay federal income tax.
• By passing business income through to shareholders’ individual income tax returns, each person’s portion is taxed at their individual tax rate, meaning the business never pays federal income tax, and it avoids the double taxation that C corporations (C corps) face.
• S corporation tax returns must be filed to generate a Schedule K-1, a tax form that’s required when filing personal taxes.

One missed tax deadline might set off a series of hefty fines and frustrations that can impact the business and every shareholder’s back pocket.

Thankfully, tax preparation can help. This guide breaks down all the important tax dates for small business owners, so you can understand the S corp filing process, hit your tax due dates, and dodge those pricey penalties.

Whether you have employees or you’re an S corp owner who regularly works for the business, you must comply with payroll tax deadlines. These filing requirements include:

• Providing a Form W-2 for each employee, including yourself, by January 31
• Filing the Annual Unemployment Tax via Form 940 by January 31
• Reporting your W-2 wages on your Form 1040
• Filing quarterly payroll taxes via Form 941, which reports income, Social Security, and Medicare employee tax withholdings

If an S corp files Form 1120-S after the deadline, the IRS enforces significant penalties, even if no tax is owed.

These penalties can include:

• Failure-to-file penalty: An S corp can be charged $225–$255 per shareholder per month or part of a month the return is late, for up to 12 months.
• Failure-to-pay penalty: S corps that owe taxes face an additional penalty of 0.5% of the unpaid tax, added for each month or part of a month, up to a maximum of 25% of the unpaid tax.
• Penalty interest: The IRS will charge interest on all penalties until they’re paid.

Late filers face heavy penalties, and fines can quickly add up. For example, a small S corp with five shareholders fails to file its business taxes on time. The IRS hits them with a base penalty of $245 per owner per month. If the company takes a few months to file, they’re facing thousands in IRS fines.

Yes, filing your small business taxes can have a direct impact on your ability to file personal taxes on time, which can trigger additional penalties for the business and the individual shareholders.

This is because each shareholder must have a Schedule K-1 form to report their portion of the business’s tax liability on their individual income tax returns (IRS Form 1040). And, K-1s are generated as part of the Form 1120-S filing process.

If no Form 1120-S is filed, no Schedule K-1 is generated, and therefore no Form 1040 can be completed.

By missing the March 15 S corp filing deadline, owners are at risk of missing the April 15 personal tax filing deadline. This can bring on additional penalties, including:

• Failure-to-furnish K-1s: S corps that don’t provide correct K-1s to shareholders on time typically face penalties of about $310 per shareholder.
• Estimated tax errors: Late K-1s can bungle estimated tax payments, leading to underpayment penalties.
• Failure-to-file penalty: Shareholders who miss the April 15 personal tax deadline face a fine of 5% of the unpaid tax for each month, or part of a month, their return is late, up to 25%.
• Failure-to-pay penalty: 0.5% of unpaid taxes for each month, reducing the failure-to-file penalty.
• Interest: The IRS will charge shareholders interest on both unpaid taxes and penalties.

The good news is you can avoid all of these penalties and subsequent problems by paying your S corp taxes on time. Mark these key deadlines on your 2026 calendar:

• January 13: Tax season starts
• February 2: Employers send W-2 forms to employees and certain 1099 forms
• March 16: S corps must file Form 1120-S for taxes or Form 7004 for a filing extension
• April 30: Q1 Form 941 due
• July 31: Q2 Form 941 due
• September 15: Standard filing extension deadline
• October 31: Q3 Form 941 due
• January 31, 2027: Q4 Form 941 due

The deadline to claim a tax refund is typically three years from when the tax return was filed or two years from when the tax was paid.

If you have questions about deadlines or tax forms, a CPA or tax professional can provide additional guidance.