How to File Form 1120: A Simple Guide for U.S. Corporations

If your business is structured as a C corporation in the US, you need to file Form 1120 every year. It reports your corporation’s income, deductions, credits, and tax liability regardless of whether you made a profit.

Unlike other business tax forms used by partnerships (Form 1065) or S corporations (Form 1120-S), Form 1120 is specifically for entities taxed as C corporations. That includes traditional corporations as well as LLCs that have elected to be treated as corporations for tax purposes.

Timely and accurate filing ensures your business remains compliant with federal tax regulations and avoids penalties for non-filing.

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Step-by-Step Process to File Form 1120 with Inkle

Filing tax forms is never easy, especially when you're managing your year-end tasks. Inkle simplifies the process to file form 1120 into a few guided steps:

Step 1 - Log in or sign up on Inkle

Head to Form 1120 filing page to start the process. If you’re a new user, sign up and create your company profile in minutes.

Step 2 - Answer a few guided questions

Share basic details about your corporation like your EIN, principal business activity, income, expenses, and officer information. The form adjusts dynamically, so you won’t have to guess what’s relevant.

Step 3 - Upload your financial documents

Inkle will prompt you to upload essential records like your Profit & Loss statement and Balance Sheet. These help populate and verify key parts of your return.

Step 4 - Review your auto-generated Form 1120

Inkle prepares the return for you - calculations, deductions, and structure are handled automatically. You'll see a completed version ready for submission.

Step 5 - Request a compliance review (optional)

Not sure about a deduction or input? You can ask Inkle’s tax team to review your return before filing.

Step 6 - Submit electronically to the IRS

Once reviewed, your return is e-filed securely through Inkle’s system. You’ll receive an official submission confirmation once it’s accepted by the IRS.

Step 7 - Access your return anytime

A copy of your filed return is saved to your Inkle dashboard, ready to download whenever needed.

Each step is designed to take the guesswork out of corporate tax filing. You don’t need to know what Schedule C or Line 27b means; Inkle handles the technicalities, flags missing details, and ensures the final form meets IRS standards. It’s filing done right, without second-guessing what’s at stake.

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Who Needs to File Form 1120?

If your business is structured as a C corporation, you're required to file Form 1120 with the IRS, even if your company had no activity or income during the year.

Here’s who must file:

i) Domestic C Corporations

Any corporation incorporated in the U.S. and taxed as a C corp must file Form 1120 annually. This includes active businesses, holding companies, and even dormant corporations. For example, a Delaware-based SaaS startup with no revenue yet but incorporated as a C corporation is still required to file.

ii) LLCs Electing C Corporation Tax Status

An LLC that has filed Form 8832 to be treated as a corporation for federal tax purposes must file Form 1120 instead of Schedule C or Form 1065. For example, a single-member tech LLC that opted for corporate taxation to attract investors would fall under this rule.

iii) U.S. Entities Owned by Foreign Companies

If a foreign company has registered a U.S. subsidiary that earns U.S.-sourced income or owns U.S. assets, that entity generally needs to file Form 1120, even if it's a pass-through operation or cost center. For example, a U.S. branch of a UK-based logistics company that earns from U.S. clients needs to file Form 1120.

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Exceptions: When You Don't File Form 1120

Not every business entity uses Form 1120. Depending on how your company is structured and taxed, you may need to file a different return:

i) S Corporations → File Form 1120-S

If your corporation has elected S corp status by submitting Form 2553 and meets eligibility criteria, you'll file Form 1120-S instead. For example, a small marketing firm with a single owner that opted for pass-through taxation would not use Form 1120.

ii) Partnerships → File Form 1065

General and limited partnerships (as well as multi-member LLCs taxed as partnerships) file Form 1065. The income passes through to individual partners via Schedule K-1. For example, a co-owned design studio operating as an LLC without corporate election would fall in this category.

iii) Sole Proprietors → File Schedule C with Form 1040

If you're running your business as an individual with no formal entity or as a single-member LLC taxed by default, you'll report income and expenses using Schedule C, not Form 1120.

Having said that when in doubt, don’t go by intuition. Even if your business feels “small” or inactive, the IRS still expects a return if you're structured as a corporation. Form 1120 is tied to your entity type, not your revenue.

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Deadlines to File Form 1120

The deadline to file Form 1120 depends on your corporation’s fiscal year but the penalties for missing it are consistent and expensive. Here’s what you need to know:

Standard Filing Deadline

• If your corporation follows the calendar year, Form 1120 is due by April 15.
• If your business follows a fiscal year, the return is due on the 15th day of the fourth month after your fiscal year ends.

Example: If your fiscal year ends on June 30, your return is due by October 15.

Filing Extension

• You can request an automatic 6-month extension by filing Form 7004 before your original due date.
• An extension to file is not an extension to pay. You must still estimate and pay any owed tax by the original deadline to avoid interest and penalties.

Penalties for Missing the Deadline

• The IRS charges a minimum penalty of $500 per month (up to 12 months) for failure to file, depending on your corporation’s gross receipts and the delay.
• Interest accrues on unpaid taxes from the original due date, regardless of whether an extension was filed.

Here’s the recommended filing timeline to avoid any penalties:-

• Early March (or one month before year-end for fiscal-year corps): Gather financials and close books
• Early April (or 2 weeks before deadline): Review and file, or apply for an extension
• Mid-October (if extended): Final filing deadline

With Inkle, filing Form 1120 is simple, accurate, and fully online. You don’t need to interpret IRS instructions, worry about deadlines, or second-guess what to include. Inkle guides you through each step by auto-filling calculations, flagging missing details, and submitting directly to the IRS.

Book a free demo and let our team walk you through the process. No paperwork. No confusion. Just compliant, stress-free filing.

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Frequently Asked Questions

1. Do I still need to file Form 1120 if my corporation didn’t earn any income?

Yes. Even if your C corporation had no revenue or activity during the year, the IRS still requires you to file Form 1120 as long as the business is active on paper.

2. What is the filing deadline for calendar-year C corporations?

If your corporation uses a calendar year, Form 1120 is due by April 15 of the following year. For fiscal-year filers, the deadline is the 15th day of the fourth month after your fiscal year ends.

3. What happens if I miss the Form 1120 deadline?

The IRS may impose a $500 or more penalty per month, up to a maximum of 12 months. Interest also accrues on any unpaid taxes from the original due date, even if you later file under extension.

4. Can I file Form 1120 for a previous year with Inkle?

Yes. Inkle supports prior-year filings. Whether you missed a deadline or are catching up on back filings, our system can help you file correctly and stay compliant.

5. Does Inkle help with state corporate income tax filings?

While Inkle focuses on federal filings (Form 1120), some states require separate corporate income tax returns. If you're unsure about your state obligations, reach out to Inkle’s team for guidance.

6. How long does it take to file Form 1120 with Inkle?

Most users complete the process in under 30 minutes, assuming their financial statements are ready. The platform handles calculations, checks for errors, and submits electronically.