Founder Education

Understanding Form 1120-S: Tax return for an S-Corporation

7 December 2023
Joshua Barnosky

Form 1120-S is a U.S. Income Tax Return form used by S-Corporations (S-corps) to report income, gains, losses, deductions, and credits to the Internal Revenue Service (IRS). A sample 1120-S form is available through the IRS website here.

What is Form 1120-S for? 

An S-corp is a corporation that elects “pass-through” taxation, a tax advantage that means the individual shareholder or shareholders and not the S-corp itself pay federal income taxes. The S-Corporation’s business income, deductions, and credits all flow through to shareholders who report this information on their tax returns. Form 1120-S is used to report these items. Additionally, a Schedule K-1 for each shareholder is included with the return, which provides their current year allocation of the above items.

If you’re not sure how your business is taxed, check with your tax preparer to see if you need to file Form 1120-S.

Who files Form 1120-S?

An S-corp files Form 1120-S itself and provides each shareholder with a copy of their Schedule K-1 to assist them in reporting their share of the S-corp’s income on their tax return.

For a corporation to be taxed as an S-corp it must complete and file Form 2553 (Election by a Small Business Corporation). Form 2553 must be submitted to the IRS for approval no more than two months and fifteen days after the beginning of the tax year the election is to take effect. Only certain corporations can make this election and must fulfill specific IRS requirements—for example, an S-corp may not have more than 100 shareholders.

How to file IRS Form 1120-S?

The due date to file Form 1120-S for the 2023 tax year is March 15, 2024. Form 7004 can be filed on or before March 15, 2024, to request an automatic extension of time to file, pushing the due date to September 16, 2024. S-Corporations can file electronically (e-file online) or physically (by mail). A tax professional or a member of your corporation can prepare the tax form.

Learn more about the 2024 business tax deadlines and important dates for corporations, LLCs, and sole proprietorships for the 2023 tax year.

Before tax season begins, you can prepare to file 1120-S by having the following information about your business ready:

Tax forms (called “schedules”) are additions to a basic tax return that apply when your business has certain types of income or deductions. In addition to the Schedule K-1, Form 1120-S may also require:

  • Schedule B: Other Information

  • Schedule K-2: Used to report items of international tax relevance from the operation of an S-Corporation

  • Schedule K-3: Used to report to shareholders their share of the items reported on Schedule K-2

  • Schedule L: Balance Sheet per Books

  • Schedule M-1: Reconciliation of Income (Loss) per Books with Income (Loss) per Return

  • Schedule M-2: Analysis of Accumulated Adjustments Account, Shareholders' Undistributed Taxable Income Previously Taxed, Accumulated Earnings and Profits, and Other Adjustments

A sample 1120-S form with all additional schedule information is available through the IRS website here.

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