Tax Depreciation vs Book Depreciation: MACRS, Section 179, and Bonus Depreciation Explained

Why Book and Tax Depreciation Differ

GAAP book depreciation is designed to match the cost of an asset to the periods that benefit from its use — the matching principle. The useful life and method are management's best estimate of how the asset's value is consumed. Tax depreciation, by contrast, is a deliberate policy tool. Congress designs MACRS rules to incentivise capital investment by allowing faster cost recovery than economic reality would justify — reducing taxes owed now and effectively subsidising business investment in productive assets.

The result: in the early years of an asset's life, tax depreciation typically exceeds book depreciation. Taxable income is lower than GAAP book income. The company pays less tax currently but will pay more in future years as book depreciation continues while tax depreciation has been fully claimed. This is the deferred tax liability explored in depth in the deferred tax accounting guide.

MACRS: The Tax Depreciation System

MACRS assigns every business asset to a recovery class with a prescribed recovery period, then applies either the 200% declining balance method (switching to straight-line when straight-line gives a larger deduction) or the 150% declining balance method to calculate the annual deduction. The applicable rates are published in IRS Rev. Proc. tables that eliminate the need to calculate rates manually for each asset.

MACRS is mandatory for most business property placed in service after 1986. It applies to tangible personal property (equipment, machinery, vehicles, computers) and real property (commercial buildings, residential rental property). It cannot be used for intangible assets, which are amortised under Section 197 of the IRC over a mandatory 15-year period.

Common Asset Recovery Periods

Notice that a 7-year MACRS asset might have a 15-year GAAP useful life, and a 39-year commercial building might be depreciated over 40 years for GAAP purposes. The tax recovery period is shorter, producing larger early-year deductions.

The Half-Year Convention

MACRS uses the half-year convention for most personal property: regardless of when during the year the asset is placed in service, only a half-year's depreciation is taken in the first year and a half-year in the final year. This simplifies the calculation and slightly reduces the first-year deduction compared to a full year. Exception: if more than 40% of all personal property is placed in service in the last quarter, the mid-quarter convention applies instead.

For real property, MACRS uses the mid-month convention: the asset is treated as placed in service in the middle of the month it was actually placed in service.

Section 179 Immediate Expensing

Section 179 of the IRC allows businesses to immediately deduct the full cost of qualifying property in the year it is placed in service — bypassing MACRS entirely — up to an annual dollar limit. For 2024, the Section 179 limit is $1,220,000 (indexed for inflation), phasing out dollar-for-dollar when total property placed in service exceeds $3,050,000. Section 179 is limited to the taxpayer's taxable income from active business — it cannot create a loss, though any unused deduction carries forward.

Qualifying property includes tangible personal property and certain improvements to nonresidential real property (roofs, HVAC, fire protection, security systems). Land and buildings themselves do not qualify.

Bonus Depreciation

Bonus depreciation (also called the special depreciation allowance) allows an additional first-year deduction on top of regular MACRS, and unlike Section 179, it is not capped and can create a tax loss. Under the Tax Cuts and Jobs Act of 2017, bonus depreciation was increased to 100% for qualified property placed in service from September 2017 through 2022 — meaning the entire cost could be deducted in year one. The bonus rate phases down after 2022: 80% in 2023, 60% in 2024, 40% in 2025, 20% in 2026, and 0% in 2027 and beyond under current law (subject to potential legislative changes).

Bonus depreciation applies automatically to qualifying new and used property; taxpayers must elect out if they prefer to use regular MACRS. Unlike Section 179, bonus depreciation is not limited by business income — it can and frequently does create large net operating losses (NOLs) in years of heavy capital investment.

How Differences Create Deferred Tax Liabilities

Because tax depreciation (MACRS + bonus + Section 179) accelerates deductions compared to GAAP book depreciation, a company in the early years of an asset's life typically reports higher GAAP income than taxable income. It pays less in current taxes than its GAAP income tax expense — the difference is a deferred tax liability that will reverse in later years when MACRS deductions run out and GAAP depreciation continues.