Tax
Tax expense bridges pre-tax income to net income. It looks like one number on the IS, but behind it sits rates, timing differences, and accounting rules that interviewers love to probe.
How Tax Expense Is Calculated
Tax expense (also called provision for income taxes) is computed on pre-tax income (EBT). The simplest version:
Tax Expense = EBT x Effective Tax Rate
But tax expense is rarely just "multiply EBT by 21%." It has two components:
- Current tax expense: The amount actually owed to the government this period
- Deferred tax expense: An accounting adjustment for timing differences between book income and taxable income
The sum of both equals total tax expense on the income statement.
The Three Tax Rates
This is where interviews get tricky. There are three rates, and they mean different things.
| Rate | Definition | Typical Use |
|---|---|---|
| Statutory rate | The rate written into law (e.g., 21% federal corporate rate in the US) | Baseline reference point |
| Marginal rate | The rate on the next dollar of income (highest bracket that applies) | Relevant for incremental decisions |
| Effective rate | Tax Expense / EBT — the actual blended rate the company paid | What you see on the IS; used in models |
"Marginal vs. effective tax rate?" Marginal = rate on the next dollar of income. Effective = Tax Expense / EBT, the blended rate actually paid. Effective is almost always lower than statutory due to deductions, credits, and timing differences.
The effective rate varies by company because of R&D credits, international structures, state taxes, and deferred tax effects. When you're building a model, you use the effective tax rate — not the statutory rate — to project tax expense.
Deferred Tax Assets and Liabilities
Companies keep two sets of books: one for the IRS (tax books) and one for shareholders (GAAP books). The rules differ, creating timing gaps in when revenue and expenses are recognized.
- Deferred Tax Liability (DTL): The company has paid less tax now than GAAP says it owes. Think accelerated depreciation — the IRS lets you depreciate faster, so taxable income is temporarily lower. You'll owe more later.
- Deferred Tax Asset (DTA): The company has paid more tax now than GAAP says it owes. Think warranty reserves — GAAP lets you expense estimated warranty costs upfront, but the IRS makes you wait until you actually pay claims.
DTAs = the government owes you later. DTLs = you owe the government later. It's purely a timing game between GAAP books and tax books — the total tax paid over time is the same.
For interviews, know three things:
- They exist because of timing differences between GAAP and tax accounting
- DTAs go on the balance sheet as assets; DTLs as liabilities
- The most common driver is depreciation (accelerated for tax, straight-line for GAAP)
Concrete example — a company buys a $100 asset with a 5-year life. GAAP uses straight-line ($20/year). The IRS allows accelerated depreciation ($30/year for years 1-2, ~$13/year for years 3-5). In years 1-2, tax depreciation exceeds book depreciation, so the company pays less tax than GAAP says it should — creating a DTL. In years 3-5, the reverse happens and the DTL unwinds. Total tax paid over 5 years is identical either way.
NOL carryforwards — if a company posts a pre-tax loss, it can't claim an immediate refund. Instead, the loss creates a Net Operating Loss (NOL) that carries forward to offset future taxable income. GAAP recognizes the future tax benefit immediately as a DTA. As the company earns profits and uses the NOL, the DTA reverses. If the company may never earn enough to use the NOL, it records a valuation allowance against the DTA.
The Tax Shield
A tax shield is any deductible expense that reduces taxable income and therefore saves cash taxes. The two most important tax shields are depreciation and interest expense.
If a company has $100M of D&A and a 25% tax rate, the depreciation tax shield saves $25M in cash taxes. This is why D&A — despite being non-cash — has real cash value. The same logic applies to interest: $40M of interest expense at 25% saves $10M in taxes, which is why debt financing is cheaper on an after-tax basis.
"Why does D&A create a tax shield if it's non-cash?" Because it's tax-deductible. It lowers taxable income, so the company pays less cash to the IRS. The cash savings equal D&A times the tax rate.
Key Takeaways
- Tax expense = current tax + deferred tax, not a simple rate times EBT
- Effective tax rate (Tax Expense / EBT) is what you use in models — it reflects the company's real tax burden
- Marginal = rate on the next dollar; effective = blended actual rate; statutory = what the law says
- Deferred taxes arise from timing differences between GAAP and tax books — the most common driver is depreciation methods
- DTAs = "government owes us later"; DTLs = "we owe the government later"
- Tax shield = deductible expense x tax rate — D&A and interest both create tax shields that save real cash