A corporation reports $2 million of pretax book income. The CFO backs out muni interest, adds back federal tax expense, adjusts for the depreciation gap, and arrives at $1.6 million of taxable income. Every adjustment fits on Schedule M-1, and the exam tests every line.
Every corporation keeps two ledgers. GAAP drives the income statement; the Internal Revenue Code drives Form 1120. The two systems measure income differently because they answer different questions: GAAP matches revenue and expense in the period earned, the Code taxes cash-realized economic gain. The gap falls into two buckets, and your job on the exam is to classify each item and push it through the M-1 in the right direction.
KEY: Permanent = never reverses = no deferred tax. Temporary = reverses later = DTA or DTL. Every M-1 question is built on this dichotomy.
A permanent difference appears in book income but never in taxable income, or the reverse. It does not reverse, it creates no deferred tax asset or liability, and its only footprint is on the effective...
Common mistakes
- Treating federal income tax expense as a temporary difference. Federal tax expense is never deductible, not now, not later. It is permanent. A $21,000 DTA on $100,000 of federal tax expense creates a balance that will never reverse.
- Reversing the depreciation direction. When MACRS exceeds book straight-line, taxable income is LOWER than book income, a SUBTRACTION on M-1. Recording a $60,000 difference as a +$60,000 addition inflates taxable income by $120,000 versus the correct answer.
- Confusing the meals limitation with a temporary difference. The 50% disallowed portion is permanent. It is an addition on M-1 and lifts the effective rate above 21%, but creates zero deferred tax. A DTA on disallowed meals will drift on the balance sheet indefinitely.
Bottom line
- Permanent differences appear in book income or taxable income, never both; they move the effective rate but create no deferred taxes.
- Temporary differences appear in both but in different years; they create DTAs (pay less later) and DTLs (pay more later).
- Federal income tax expense is always permanent and always an M-1 addition; the balance never reverses.
- Schedule M-1 reconciles book net income to taxable income for corporations under $10 million in total assets; additions raise it, subtractions lower it.
Exam shortcut
When an M-1 question lists six items, sort them into two piles before doing arithmetic: additions on the left (federal tax expense, nondeductible items, prepaid income taxed now) and subtractions on the right (tax-exempt income, life insurance proceeds, excess tax depreciation). Add and subtract in one pass. Remember: Permanent = no deferred tax = effective rate only. Temporary = DTL or DTA.
The full lesson (about 2,600 words, 17 min read) adds 2 worked examples, all 6 common mistakes, a self-check, free in the app.
Learning objectives
- V.A1
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