How to File Your U.S. Corporate Tax Return (Form 1120)

April 3, 2025

Syed Kausar

Every U.S. corporation — whether profitable or not — must file an annual corporate income tax return. For most businesses, this means IRS Form 1120 (C-Corporations) or Form 1120-S (S-Corporations). But corporate tax isn't just about compliance’ It's about choosing the right entity structure, planning deductions strategically, and avoiding IRS pitfalls that could cost thousands. At ADYZER, we provide comprehensive corporate tax services tailored to help businesses grow while staying fully compliant.

Who Must File a Corporate Tax Return?

C-Corporations

Must file Form 1120 annually, even with no income

S-Corporations

Must file Form 1120-S, passing profits/losses to shareholders

LLCs

May be taxed as a sole proprietorship, partnership, or corporation depending on elections

Foreign-Owned Corporations

Required to file if engaged in U.S. trade or business

Failure to file can trigger IRS penalties, back taxes, and loss of good standing with state authorities.

Key Filing Deadlines (2024–2025)

April 15, 2025

Standard deadline for calendar-year C-Corps

March 15, 2025

Standard deadline for S-Corps and Partnerships

Extension

File Form 7004 for a 6-month extension

Estimated Payments

Required quarterly if expected tax exceeds $500

Penalties for Late Filing or Payment

Late Filing

5% of unpaid tax per month (up to 25%)

Late Payment

0.5% per month, plus daily interest

Information Return Penalties

Missing Schedule K-1 (S-Corps) or shareholder info can cost $210 per shareholder per month

U.S. Corporate Tax Rates

C-Corporations

Flat 21% federal rate

State Corporate Income Taxes

Range from 0% (South Dakota, Wyoming) to 11.5% (New Jersey)

S-Corporations & Partnerships

Pass-through entities — income reported on owners' personal returns

Deduction & Credit Opportunities for Corporations

Many corporations overpay taxes by missing deductions and credits. ADYZER ensures you capture every benefit.

Key Deductions

Business Expenses: Payroll, rent, utilities, marketing, insurance

Depreciation (MACRS): Accelerated depreciation for assets

Section 179 Deduction: Immediate write-off for eligible equipment

Officer Compensation: Deductible if reasonable and documented

Charitable Contributions: Up to 10% of taxable income

Key Credits

R&D Tax Credit (IRS Research Credit) – up to 20% of eligible R&D costs

Work Opportunity Tax Credit (WOTC): For hiring employees from targeted groups

Energy Efficiency Credits: For renewable energy investments

Common IRS Mistakes in Corporate Returns

Misclassifying active vs. passive income

Incorrect depreciation schedules

Failing to track multi-state nexus obligations

Inadequate shareholder records for S-Corps

Overstating deductions without documentation

These mistakes often lead to IRS audits and penalties.

Special Considerations for International Corporations

GILTI Tax (Global Intangible Low-Taxed Income)

Applies to controlled foreign corporations

BEAT (Base Erosion and Anti-Abuse Tax)

Affects corporations with foreign affiliate payments

Transfer Pricing Rules

IRS scrutiny on intercompany transactions

Foreign Tax Credits

Prevents double taxation if properly claimed

ADYZER's Corporate Tax Advantage

At ADYZER, we go beyond filing — we create tax strategies that protect your business and unlock savings.

Our Approach

Entity Structuring

Optimize choice between C-Corp, S-Corp, or LLC

Tax Planning

Identify deductions, credits, and income-splitting strategies

IRS Compliance

Complete Form 1120/1120-S and all schedules

Audit Defense

Direct representation with the IRS or state agencies

Cross-Border Expertise

For corporations with Canadian or international operations

FAQs About U.S. Corporate Tax

Can an LLC file Form 1120?

Yes, if the LLC elects to be taxed as a corporation. Otherwise, it files as a partnership or sole proprietorship.

Do corporations file even if no income?

Yes, all corporations must file, even if inactive or at a loss.

Can a C-Corp switch to an S-Corp?

Yes, by filing Form 2553, but restrictions apply (shareholder limits, stock class rules).

What if my business operates in multiple states?

You may owe taxes in each nexus state. ADYZER manages multi-state compliance.

Take Action

Don't let corporate tax filing become a liability. With ADYZER, your business gains expert tax planning, compliance, and IRS representation.