Corporate Income Tax

The corporate income tax is the federal (and sometimes state) levy on a business’s profits. In the US, the federal rate was cut from 35% to 21% in 2018. Like any tax, it influences where companies invest, how they finance themselves, and what profits they return to shareholders. A high corporate tax encourages debt (interest is deductible) and discourages equity investment; a low rate can stimulate capital spending but reduces government revenue.

How corporate income tax is calculated

A corporation reports gross revenue, subtracts cost of goods sold (COGS), operating expenses, depreciation, amortization, and interest expense, arriving at taxable income. The corporation pays tax on that income at the statutory federal rate (21% in the US), plus any applicable state and local taxes.

Unlike dividends or capital gains, corporate income tax is not graduated. A small firm and a large firm pay the same marginal rate on incremental profit. This is a contrast to individual income tax, which is progressive.

Interest deductibility and leverage bias

The most consequential feature is that interest expense is fully deductible, while dividend payments to shareholders are not. This creates a bias toward debt financing over equity financing.

A company that borrows $100 million at 5% pays $5 million annually in interest, reducing taxable income by $5 million. At a 21% tax rate, the tax savings are $1.05 million. A company that raises $100 million in equity and pays 5% dividends ($5 million per year) gets no tax deduction. The dividend is paid from after-tax income.

Over decades, this preference for debt has increased corporate leverage and financial fragility. Companies borrow more aggressively than they would if interest were not deductible.

Depreciation and tax incentives

Depreciation is a deduction that reduces taxable income without a cash outflow, allowing companies to defer taxes on capital investments. Bonus depreciation and Section 179 deductions accelerate depreciation in early years, providing additional tax relief for capital-intensive businesses.

These provisions incentivize capital expenditure (capex). A company investing in a factory can deduct the cost faster, reducing its tax bill and improving cash flow. The policy goal is to encourage productive investment; critics argue it is often gamed via sale-leasebacks and other tax minimization strategies.

The “double taxation” problem

Profits earned by a corporation are taxed at the corporate rate. When those profits are distributed as dividends, they are taxed again at the shareholder level (at the individual capital gains rate, currently up to 20% federal). This “double taxation” is a long-standing critique of the corporate tax.

Some argue the cost is overstated (dividends are only taxed if paid; retained earnings boost stock price, triggering capital gains on sale instead). Others argue the structure is inefficient and depresses capital allocation to productive uses.

Pass-through entities (S-corps, partnerships, LLCs) avoid the corporate tax by passing income directly to owners’ personal returns, taxed once at individual rates. This is why many smaller and medium-sized firms choose pass-through structure.

Tax rate changes and market impact

The 2017 Tax Cuts and Jobs Act reduced the US corporate rate from 35% to 21% and provided bonus depreciation. The cut was intended to boost investment and growth. Stock markets rallied on the news; companies reported higher earnings per share (EPS) due to lower tax bills.

However, empirical evidence on whether lower corporate rates lead to sustained increases in capex is mixed. Some companies used tax savings to fund share buybacks and dividends rather than reinvestment. Others did invest, but the relationship between the rate cut and actual growth was weaker than proponents had predicted.

International arbitrage and “Double Irish Dutch Sandwich”

Multinational corporations exploit differences in tax rates across countries. The infamous “Double Irish Dutch Sandwich” allowed companies to shift profits to low-tax jurisdictions (Ireland, Netherlands) using intellectual property transfers and management fees, reducing global tax liability.

In response, the OECD initiated a “Base Erosion and Profit Shifting” (BEPS) initiative, and in 2021, the G7 agreed to a global minimum corporate tax of 15%. This is intended to reduce incentives for aggressive international tax planning, though implementation has been slow.

Alternative Minimum Tax (AMT)

The corporate AMT is a parallel tax system designed to ensure corporations pay at least some minimum tax even if standard deductions, credits, and depreciation reduce regular taxable income to zero. The AMT is calculated on “book income” (accounting income) with adjustments, then taxed at a lower rate (20%). If the AMT exceeds regular tax, the corporation pays the AMT.

The AMT has become less relevant after the 2017 rate cut, as it is now harder for large profitable companies to reduce their regular tax liability below the AMT.

State and local corporate taxes

Most states impose a corporate income tax (typically 3–7%). A few states (Texas, Wyoming, Nevada, South Dakota) have no corporate income tax but may have alternatives like gross receipts taxes or capital gains taxes.

Some cities and counties impose business taxes or payroll taxes. A company’s total effective tax rate often exceeds the federal 21% when state, local, and foreign taxes are factored in.

Policy debates

Revenue and fairness: Critics argue the 21% rate is already low and that corporations should pay more to fund infrastructure and services. Supporters argue the rate is competitive globally and that lower rates stimulate growth, which broadens the tax base and partially offsets revenue losses.

Competitiveness: Multinationals with significant US operations face a 21% federal rate plus state/local taxes, potentially exceeding 25%. Some argue this puts US companies at a disadvantage against foreign competitors with lower home-country tax rates.

Complexity: The corporate tax code is thousands of pages long, with numerous credits, deductions, and preferences. Many argue the code should be simplified (lower rate, fewer loopholes). Others argue certain incentives (R&D credits, energy transition credits) serve important policy goals.

Impact on market valuation

The corporate tax rate affects after-tax earnings, which feed into valuation multiples. A rate cut increases EPS without a change in operational performance, often leading to stock price increases. Conversely, a rate increase reduces EPS and can pressure valuations, absent a corresponding improvement in growth.