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Glossary/Tax and regulatory

Book-tax differences

Book-tax differences arise when GAAP income differs from taxable income because of timing items that reverse and permanent items that never do, reconciled on Schedule M-1 or M-3.

CORAA TeamUpdated November 5, 2026

Definition

Book-tax differences are the gaps between pre-tax income under GAAP and taxable income under the Internal Revenue Code. Temporary differences (accelerated tax depreciation, accruals deductible when paid, reserves) reverse over time and create deferred taxes. Permanent differences (nondeductible fines, the nondeductible part of meals, tax-exempt interest) never reverse and affect the effective tax rate. Corporations reconcile book income to taxable income on Schedule M-1, and corporations with total assets of $10 million or more file the more detailed Schedule M-3.

Why it matters in an audit or review

Auditors use the differences to test the tax provision and deferred taxes, compare the return to the provision, and identify unusual items that point to missing accruals or aggressive positions.

Example

(Illustrative) GAAP pre-tax income is $400,000. Tax depreciation exceeds book by $60,000 (temporary), and nondeductible penalties are $5,000 (permanent). Taxable income is 400,000 - 60,000 + 5,000 = $345,000.

Common mistakes

  • Recording deferred taxes on permanent differences.
  • Not updating the provision after the return is filed.

Sources

  • FASB ASC 740-10, Income Taxes, Overall (temporary and permanent differences)
  • IRS, Instructions for Schedule M-3 (Form 1120) and Schedule M-1 (Form 1120); corporations with total assets of $10 million or more file Schedule M-3
  • IRS, About Schedule M-3 (Form 1120), https://www.irs.gov/forms-pubs/about-schedule-m-3-form-1120

Definitions paraphrase AICPA and FASB guidance; read the standard itself before relying on a requirement. Example figures are illustrative. This page is guidance, not professional advice. Report an error

Standards

ASC 740

Related terms

  • Deferred tax assets and liabilities
    Deferred tax assets and liabilities capture the future tax effects of temporary differences between book and tax bases, measured at enacted tax rates under ASC 740 and classified as noncurrent.
  • Effective tax rate reconciliation
    An effective tax rate reconciliation explains the difference between expected tax at the statutory rate and reported income tax expense, and is a key analytical check on the tax provision.
  • Income tax basis of accounting
    Income tax basis financial statements follow the rules the entity uses to compute taxable income, a common special purpose framework for partnerships and small businesses that do not need GAAP statements.

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