Your Complete Corporate and S-Corp Income Tax Guide

Corporate Tax Forms, Tax Rates, Tax Filing Information

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U.S. corporations are complex entities, and their taxes are even more so. They're a special kind of business because, unlike other businesses, they're a separately taxpaying entity. Corporations are owned by their shareholders. They pay taxes on earned income, then their shareholders are taxed on the dividend they receive.

Keeping a few main considerations in mind will help you prepare for corporate taxes, including types of corporations and how they're taxed, when and where to file, which form to use, and how to estimate your corporate taxes.

Key Takeaways

  • These businesses use articles of incorporation to incorporate within their state or in multiple states.
  • The Tax Cuts and Jobs Act made multiple changes to the tax rules that apply to these business entities.
  • Corporations use IRS Form 1120 to file their taxes.
  • S-corporations use IRS Form 1120-S. Profits and losses are passed through to the shareholders' personal tax returns.

U.S. Corporations and Income Taxes

There are two basic types of corporations in the U.S.: C corporations and S corporations. C corps are typically just called "corporations." S corporations are named for the section of the Internal Revenue Code that applies to this business type. Both have the same basic structure,

Corporate Tax Rate Reduction and Other Changes

The Tax Cuts and Jobs Act made some changes that affected corporations and S corporations when it went into effect in 2018. The biggest change was the elimination of the tax schedule and a flat corporate income tax rate of 21% of corporate net income.

Other tax law changes affecting corporations include both benefits and drawbacks:


The change in the corporate tax rate didn't affect S corporations because their owners are taxed on earnings on their personal tax returns.

Tax Return Due Dates

Corporations with a Dec. 31 year-end have a tax return filing deadline of April 15.  The tax return is due on the 15th day of the fourth month after year-end for corporations with a fiscal year-end other than Dec. 31. The only exception is when a corporation's fiscal year ends on June 30. The corporation must file tax returns by the 15th day of the third month after year-end (Sept. 15) in this case.

S corporations must usually take a calendar year-end date (Dec. 31) to agree with the personal tax year-end unless it can establish a reasonable business purpose for a different date. The filing date and tax return due date are the 15th day of the third month after the tax year-end. In other words, taxes are due March 15 for almost all S corporations.

Tax Forms for Corporations and S Corporations

Corporations file their taxes on Form 1120. S corporations file their federal income taxes using Form 1120-S. S corporation shareholders report their share of corporate income or loss on a Schedule K-1, Shareholder's Share of Income, Deductions, Credits, with their personal returns.

You can file your corporate or S corporation tax return by mail, or you can have your tax preparer e-file it. Certain corporations with assets of $10 million or more that file at least 250 returns per year must e-file. You can find the correct addresses to use when filing your Form 1120 on the IRS website.

You'll have to provide some financial reports and other documents to your tax preparer to file your corporate or S corporation income tax return. These documents include information about the cost of goods sold, dividends, and many other aspects of operating a corporation.


See the Instructions for Form 1120 for more details on filing your corporate tax return.

Estimated Taxes, Amended Tax Returns, and Extension Applications

Corporations must pay estimated taxes if their expected tax bill is $500 or more. They calculate and file estimated taxes on IRS Form 1120-W. The installments are generally due by the 15th day of the fourth, sixth, ninth, and twelfth months of the tax year. This would be April 15, June 15, September 15, and December 15 for a corporation that uses the calendar year.

Corporations receive automatic approval on extension applications, but they must still file the application using Form 7004. The form must be filed by the due date of the corporate tax return, and they must pay any taxes due by this date.

A corporation must use Form 1120x if it needs to amend a previous year's tax return.

Getting Help with Corporate Income Taxes

Income taxes for corporations and S corporations are complicated. It's usually best to get help from a CPA or tax professional who is familiar with corporate taxes rather than attempt to prepare this return on your own. Review basic information about business taxes that you should know before you enlist the help of a CPA, enrolled agent, or another qualified tax preparer to prepare your corporation's taxes.

Frequently Asked Questions (FAQs)

What steps are required to form a corporation?

Corporations are formed at the state level. The process involves drafting articles of incorporation and corporate bylaws, electing a board of directors, and adhering to the state's registration requirements. An S corporation is created first as a C corporation, then it files to elect S corporation status with the IRS.

Do corporations have to pay taxes at the state level?

Corporations must also pay income taxes to the state or states where the business is incorporated if these states have corporate taxes. Go to the website of your state's department of revenue or similar agency to find out more about your state's corporate tax rates and filing instructions.

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  1. Internal Revenue Service. "Publication 542 Corporations." Page 2.

  2. Internal Revenue Service. "Publication 542 Corporations."

  3. Internal Revenue Service. "Tax Cuts and Jobs Act: A Comparison for Businesses."

  4. Internal Revenue Service. "IRS Issues Guidance on the Elimination of the Deduction of Qualified Transportation Fringe Benefit Expenses."

  5. Internal Revenue Service. "Publication 509 Tax Calendars."

  6. Internal Revenue Service. "Tax Years."

  7. Internal Revenue Service. "Instructions for Form 1120-S U.S. Income Tax Return for an S Corporation." Page 3.

  8. Internal Revenue Service. "E-File for Large Business and International (LB&I)."

  9. Internal Revenue Service. "Instructions for Form 1120-W." Page 1.

  10. Internal Revenue Service. "Publication 542 Corporations." Page 6.

  11. Internal Revenue Service. "S Corporations."

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