Ch3. Corporate Income Tax — The Structure of Business Taxation

What Is Corporate Income Tax?

Corporate income tax: A tax on the income of a corporation (C-corp) or other taxable entity (certain trusts and associations).

A corporation is a separate legal taxpayer from its owners. The corporation’s income is taxed at the corporate level, and shareholders are taxed again on dividends received — this is the double taxation problem. The dividends-received deduction (DRD) (IRC § 243) partially mitigates this for intercorporate dividends.

Who Pays Corporate Tax?

Domestic corporations: Incorporated in the US → taxed on worldwide income
Foreign corporations: Taxed only on US-source income (effectively connected income)
Pass-through entities (S-corps, partnerships, LLCs) are generally not subject to corporate tax; income passes through to owners

Computing Corporate Taxable Income

Corporate tax = Gross Income − Allowable Deductions (IRC §§ 61, 162).

In practice, corporations reconcile their book income (GAAP) with taxable income (tax law) because the two sets of rules differ. This reconciliation is reported on Schedule M-1 (or M-3 for large corporations) of Form 1120.

GAAP net income (book income)
  + M-1 add-backs:
      Items in book income but NOT in taxable income (e.g., tax-exempt interest)
      Items deducted for book but NOT deductible for tax (e.g., fines, 50% meals)
  − M-1 subtractions:
      Items taxable but not in book income
      Items deductible for tax but not expensed in books
= Taxable income before special deductions
  − Net operating loss (NOL) deduction
  − Dividends-received deduction (DRD)
= Taxable income
  × 21% tax rate
= Tax liability
  − Tax credits
= Net tax due

Deductions and Non-Deductible Items

Deductions (IRC § 162)

Ordinary and necessary business expenses are deductible. The key standard is that the expense must be:

Ordinary (common and accepted in the trade or business)
Necessary (helpful and appropriate for the business)

Non-deductible items (book-tax differences):

Federal income tax itself (IRC § 275)
Business entertainment expenses: Non-deductible post-TCJA (§ 274(a)(1))
Meals: Only 50% deductible (§ 274(n))
Fines and penalties: Non-deductible (§ 162(f))
Lobbying and political contributions: Non-deductible (§ 162(e))
Excessive compensation to “covered employees”: Amount exceeding $1M non-deductible (§ 162(m))
Related-party expenses above market rate: Subject to recharacterization
Club memberships for entertainment: Non-deductible

Depreciation

Depreciation (cost recovery): Deducting the cost of business assets over their useful lives.

Under the Modified Accelerated Cost Recovery System (MACRS) (IRC § 168), the IRS prescribes asset classes and recovery periods:

Asset Class	Recovery Period
Office furniture, computers	5–7 years
Machinery and equipment	5–7 years
Nonresidential real property	39 years
Residential rental property	27.5 years
Land improvements	15 years

Section 179 expensing (IRC § 179): Allows immediate deduction of qualifying assets up to ** $1,220,000** (2024 limit). Phases out dollar-for-dollar when asset purchases exceed$ 3,050,000.

Bonus depreciation (IRC § 168(k)): Additional first-year deduction — 60% in 2024, phasing down to 0% by 2027 under TCJA rules.

Business Meals and Entertainment

Post-TCJA rules substantially limited these deductions:

Business meals: 50% deductible (if directly related to business)
Entertainment (sporting events, concerts, etc.): 0% deductible
Employee meals provided at the workplace: 50% (was 100% before 2018)

The 50% rule means the disallowed half is a permanent book-tax difference — it reduces book income but doesn’t reduce taxable income.

Federal Corporate Tax Rate

Post-TCJA flat rate:

Taxable Income	Rate
All amounts	21%

The pre-2018 graduated rate structure (15%–35%) was eliminated. The 21% flat rate applies to all C-corporations.

State corporate income taxes vary (0%–12%) and are deductible on the federal return, reducing the effective federal rate slightly.

Net Operating Loss (NOL)

When a corporation’s deductions exceed its income, the resulting NOL can reduce future tax:

Post-2017 NOLs: Carried forward indefinitely; deduction limited to 80% of taxable income each year
Pre-2018 NOLs: Can be carried back 2 years or forward 20 years under prior law

Example:
2024 taxable loss: ($100,000) → creates $100,000 NOL
2025 taxable income: $300,000
→ NOL deduction: $100,000 × 80% = $80,000 (can deduct $80,000)
→ 2025 taxable income after NOL: $220,000
→ Remaining NOL: $20,000 carries forward

Tax Credits and Incentives

R&D Tax Credit (IRC § 41)

Credits for qualified research expenses incurred in the US:

Regular credit: 20% of qualifying expenses above a base amount
Alternative simplified credit: 14% of qualifying expenses above 50% of the average of the prior 3 years

Section 199A — Qualified Business Income Deduction

For pass-through entities (not C-corps): up to 20% deduction of qualified business income. Significant for S-corp owners, partners, and sole proprietors.

Employment Credits

Work Opportunity Tax Credit (WOTC): Credit for hiring from targeted disadvantaged groups
Paid Family and Medical Leave Credit (§ 45S): Credit for offering paid FMLA leave
Employee Retention Credit (ERC): Post-COVID credit for retaining employees (2020–2021)

Corporate Tax Filing

Filing deadline: 15th day of the 4th month after year-end → April 15 for calendar-year corps (Form 1120)
Extension: 6-month extension available (to October 15) via Form 7004
Estimated taxes: Corporations must make quarterly estimated payments (April 15, June 15, September 15, December 15) or face underpayment penalties
IRS audit cycles: Large corporations (assets $10M+) face the highest audit scrutiny; smaller businesses are audited less frequently but face risk when returns show unusual deductions

Learning Checklist

Explain the corporate tax computation from book income through net tax due (Schedule M-1 reconciliation)
Name four categories of non-deductible expenses under the IRC
State the current federal corporate tax rate and when it took effect
Explain the post-TCJA NOL rules (indefinite carryforward, 80% limit)
Describe the R&D Tax Credit and how it encourages innovation

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