Filing taxes for an S corporation requires submitting Form 1120-S to the IRS, which reports the company’s income, deductions, and credits for the year. Unlike a C corporation, the S corp itself generally doesn’t pay federal income tax. Instead, profits and losses pass through to shareholders, who report them on their personal returns. That pass-through structure simplifies some things but creates a multi-step filing process you need to get right.
Form 1120-S and Supporting Schedules
Form 1120-S is the core return for every S corporation. It captures the business’s total revenue, cost of goods sold, deductions (rent, salaries, depreciation, etc.), and net income or loss. Even if the company had no activity during the year, you still need to file.
Along with the main form, you’ll likely need several supporting schedules:
- Schedule K-1: One for each shareholder, showing their individual share of the corporation’s income, deductions, and credits. The S corp files copies with the IRS and sends one to every shareholder.
- Schedule D: Required if the corporation sold or exchanged capital assets, or distributed appreciated assets to shareholders.
- Schedule B-1: Used when any shareholder is a trust, estate, disregarded entity, or nominee rather than an individual.
- Schedule K-2 and K-3: Only needed if the S corp has items of international tax relevance, such as foreign income or foreign tax credits.
- Schedule M-3: Required only for S corporations with total assets of $10 million or more, reconciling financial statement income to taxable income.
Most small S corps with a handful of domestic shareholders will file Form 1120-S, the Schedule K-1s, and possibly Schedule D. The international and large-asset schedules won’t apply.
Filing Deadlines and Extensions
Form 1120-S is due on the 15th day of the third month after the corporation’s tax year ends. For a calendar-year S corp, that means March 15. If that date falls on a weekend or holiday, the deadline shifts to the next business day.
If you need more time, file Form 7004 before the original deadline to get an automatic six-month extension, pushing the due date to September 15 for calendar-year filers. The extension gives you extra time to file the return, but it does not extend the time for shareholders to file their personal returns (due April 15). Because shareholders need their K-1s to complete their own returns, late S corp filings can create a chain reaction of personal extensions too.
Late filing carries a penalty of roughly $220 per shareholder per month the return is overdue, up to 12 months. For a four-shareholder S corp that’s three months late, that adds up to about $2,640.
Paying Yourself a Reasonable Salary
If you’re a shareholder who also works in the business, the IRS requires you to pay yourself a reasonable salary before taking additional money as distributions. Salary is subject to payroll taxes (Social Security and Medicare), while distributions are not. That tax difference is exactly why the IRS pays close attention: setting your salary artificially low to avoid payroll taxes is one of the most common S corp audit triggers.
There’s no fixed formula for what counts as “reasonable.” Courts have evaluated it on a case-by-case basis using factors like your training and experience, the duties you perform, time and effort devoted to the business, what comparable businesses pay for similar roles, the company’s dividend history, and how non-shareholder employees are compensated. A good starting point is researching what someone with your skills and responsibilities would earn in a similar position at another company.
Run payroll for yourself throughout the year, withhold income taxes and the employee share of FICA, and pay the employer share. At year end, you’ll issue yourself a W-2 just like any other employee. Only after covering a reasonable salary should remaining profits be taken as shareholder distributions.
How Profits Flow to Your Personal Return
After the S corp files Form 1120-S, each shareholder receives a Schedule K-1 detailing their share of the company’s income, losses, deductions, and credits. You report these amounts on your personal Form 1040, typically on Schedule E (Supplemental Income and Loss). Your share of the income is taxable to you whether or not the company actually distributed cash to you during the year.
You’re required to report the K-1 items consistently with how the corporation treated them on its return. If you spot an error on your K-1, don’t change it yourself. Notify the corporation and request a corrected version, which the company must also send to the IRS. If you can’t get a correction and file your personal return inconsistently with the K-1, you’ll need to attach Form 8082 to explain the discrepancy.
Loss Limitations to Watch
If the S corp had a loss, you can’t always deduct the full amount on your personal return. Four limitations apply, and you must work through them in order:
- Basis limitation: You can only deduct losses up to your tax basis in the S corp, which includes your original investment plus accumulated income minus prior distributions and losses.
- At-risk limitation: Your deductible loss is further limited to the amount you have economically at risk in the business.
- Passive activity limitation: If you don’t materially participate in the business, losses may be classified as passive and can only offset other passive income.
- Excess business loss limitation: Even after passing the first three tests, there’s a cap on total business losses you can deduct against non-business income in a single year.
Losses that exceed any of these thresholds aren’t gone forever. They’re typically suspended and carried forward to future years when you have sufficient basis, at-risk amounts, or passive income to absorb them.
The Qualified Business Income Deduction
S corp shareholders have been eligible for the qualified business income (QBI) deduction, which allows you to deduct up to 20% of your share of the business’s qualified income on your personal return. This deduction was created by the Tax Cuts and Jobs Act and applies to tax years beginning after December 31, 2017, and ending on or before December 31, 2025.
One important detail: your W-2 salary from the S corp does not count as QBI. Only the pass-through business income reported on your K-1 qualifies. This creates a natural tension with the reasonable salary requirement. Paying yourself more in salary reduces the income eligible for the 20% deduction, while paying too little invites IRS scrutiny. The right balance depends on your specific situation.
As of this writing, the QBI deduction is set to expire after the 2025 tax year. If Congress does not extend it, the deduction will not be available for 2026 and beyond. Check current law before relying on it for your filing year.
State Filing Requirements
Most states require a separate S corp tax return, and the rules vary significantly. Some states honor the federal S election automatically, while others require you to file a separate state-level S election. A handful of states impose an entity-level tax on S corporations, meaning the business itself owes state income tax even though it doesn’t owe federal income tax. Franchise taxes or minimum annual taxes may also apply regardless of whether the business earned a profit. Check your state’s department of revenue for specific forms, deadlines, and tax rates.
Steps to Complete the Filing
Pulling together an S corp return is more involved than filing a personal return, but the process follows a logical sequence:
- Gather financial records: You’ll need a complete set of books for the year, including a profit and loss statement, balance sheet, and records of all shareholder distributions, contributions, and loan activity.
- Run final payroll: Make sure all shareholder-employee salaries are finalized, W-2s are issued, and payroll tax returns (Form 941 quarterly, Form 940 annually) are filed.
- Prepare Form 1120-S: Report income, deductions, and credits on the main form. Complete the balance sheet (Schedule L) and the reconciliation of income per books with income per the return (Schedule M-1 or M-3).
- Generate Schedule K-1s: Allocate each shareholder’s pro rata share of income, losses, and credits based on ownership percentage and number of days owned during the year.
- Distribute K-1s to shareholders: Shareholders need these to file their personal returns, so aim to get them out well before the April 15 individual deadline.
- File the return: Submit Form 1120-S electronically or by mail by March 15 (for calendar-year filers), or request an extension using Form 7004.
- File state returns: Complete any required state S corp returns by their respective deadlines, which may differ from the federal due date.
Most S corp owners use tax software designed for business returns or hire a tax professional, especially in the first year. The interaction between the corporate return, payroll, K-1 allocations, and your personal return has enough moving parts that even small errors can cascade. If you’re doing it yourself, business tax software will walk you through Form 1120-S line by line and auto-generate the K-1s from the data you enter.