Ch8. Tax Intro — Corporate Income Tax Basics

What Is Corporate Income Tax?

Corporate income tax is the tax imposed on the income earned by a corporation (C-corp, S-corp, LLC taxed as a corporation, etc.). Just as individuals pay individual income tax, corporations pay corporate income tax.

Corporate taxpayers:
- Domestic corporations: incorporated in the US or managed/controlled in the US
- Foreign corporations: taxed only on US-source income (effectively connected income)

Corporate income tax is governed primarily by Subchapter C of the Internal Revenue Code (IRC §§ 301–385) and administered by the IRS.

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Types of Corporate Taxable Income

Corporate income subject to tax includes:

Income Type	Description
Ordinary business income	Profit from regular business operations
Capital gains	Gains from the sale of capital assets
Passive income	Rental and certain investment income

In practice, ordinary business income from operations is the primary focus.

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Calculating Corporate Taxable Income

Basic Structure

Taxable Income = Gross Income − Allowable Deductions

Gross Income: all income from whatever source derived (IRC § 61)
Deductions: ordinary and necessary business expenses (IRC § 162)

Starting from book net income, corporations make adjustments under the tax code (M-1 and M-3 reconciliation on Form 1120).

Tax Reconciliation (Schedule M-1):
Book net income
+ Book income not included in taxable income (add-backs)
+ Non-deductible book expenses
− Tax deductions not in book income
− Book income items exempt from tax
= Taxable income

Key Non-Deductible Items

Items the IRS does not allow as business deductions:

• Meals & entertainment: only 50% of meals deductible; entertainment generally non-deductible (Tax Cuts and Jobs Act 2017)
• Excessive compensation: unreasonable executive pay disallowed
• Personal expenses: owner’s personal spending mixed into business
• Depreciation above MACRS limits: excess depreciation under §168
• Related-party interest: above-market interest to related parties (§163(j) limits)

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Corporate Tax Rates

Under the Tax Cuts and Jobs Act of 2017 (TCJA), the US moved to a flat corporate tax rate:

Federal Corporate Tax Rate: 21% (flat rate, IRC § 11)

Prior to TCJA (before 2018), graduated rates of 15%–35% applied. The flat 21% rate now applies to all C-corporations regardless of income level.

State Corporate Income Taxes

Most states also impose corporate income tax. Combined federal + state effective rates vary:

Example combined effective rate:
Federal: 21%
State (varies): 0%–12% (e.g., California 8.84%, Texas 0%)
Combined effective rate: ~21%–30%+ depending on state

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Key Tax Credits and Incentives

Research & Development (R&D) Tax Credit

Corporations investing in qualified research activities can claim the R&D Tax Credit (IRC § 41):

Credit = 20% of qualified research expenses above a base amount
(Alternative simplified credit: 14% of qualified expenses above 50% of 3-yr avg)

Work Opportunity Tax Credit (WOTC)

A credit for hiring individuals from targeted groups (veterans, SNAP recipients, etc.):

WOTC = 40% of first-year wages (up to $6,000 per eligible employee)
= up to $2,400 per hire

Small Business Deduction (§ 199A)

Pass-through entities (S-corps, partnerships, sole proprietors) may deduct up to 20% of qualified business income (QBI) — a significant benefit for non-C-corp businesses.

Foreign Tax Credit

Corporations paying tax abroad can claim a Foreign Tax Credit (IRC § 901) to avoid double taxation on the same income.

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Net Operating Loss (NOL) Carryover

When a corporation has a tax loss, it can carry the loss forward to offset future profits:

Post-TCJA NOL rules (for losses arising after 2017):
- No carryback (generally)
- Carry forward indefinitely
- Limited to 80% of taxable income in any carryforward year

Example:
2024 loss: $100,000
2025 income: $300,000
→ 2025 taxable income: $300,000 − $80,000 (80% limit) = $220,000

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Sole Proprietorship vs. Corporation

A critical decision when starting or growing a business:

Feature	Sole Proprietor / LLC	C-Corporation
Taxpayer	Individual owner	The corporation itself
Tax type	Individual income tax (10%–37%)	Corporate tax (21%)
Top federal rate	37% + 15.3% SE tax	21% (+ dividend tax on distributions)
Owner salary	Not deductible	Deductible as wages
Losses	Directly offset personal income	Carry forward 80%
Formation cost	Minimal	State filing fees + legal costs
Liability	Unlimited (sole prop)	Limited to investment
QBI deduction	Up to 20% deduction available	Not applicable

When to consider incorporating: When annual net profit exceeds ~$100,000–$200,000, the math often favors an S-corp or C-corp structure for tax efficiency.

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Corporate Tax Filing and Payment

Filing Deadline

Corporations must file Form 1120 (C-corp) or Form 1120-S (S-corp):

Calendar-year corporations: April 15 (6-month extension to October 15 available)
Fiscal-year corporations: 15th day of the 4th month after year-end

Estimated Tax Payments

Corporations must pay estimated taxes quarterly:

Quarterly estimated payments due:
April 15, June 15, September 15, December 15

Safe harbor: pay 100% of prior year's tax liability
(or 100% of current year liability to avoid underpayment penalty)

Installment Payments

If the final tax bill is large, the IRS allows spreading payment across the quarterly installments — no separate installment arrangement needed if estimates were accurate.

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Corporate Formation and Tax Planning

Formation Steps

1. Choose entity type (C-corp, S-corp, LLC) and state of incorporation
2. File Articles of Incorporation with the state
3. Obtain EIN from the IRS (Form SS-4)
4. Register for state and local taxes
5. Open a business bank account and establish payroll (if applicable)

Family Business Tax Strategy

Paying reasonable salaries to family members who work in the business is a legitimate way to shift income to lower-bracket taxpayers. The salary must reflect actual services rendered:

Important: Salaries to family members who don't actually work
in the business are not deductible and may constitute fraud.

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Key Takeaways

Item	Key Point
Federal corporate rate	21% flat (post-TCJA)
Taxable income	Gross income − allowable deductions
Filing deadline	April 15 (calendar year); Form 1120
Key credits	R&D credit, WOTC, foreign tax credit
Sole prop vs. corp	Corporation often better above ~$100K+ net profit

Corporate taxation is complex, but accurate reporting and maximizing available deductions and credits can significantly reduce a business’s tax burden. Working with a qualified CPA or tax attorney is strongly recommended.