Straight-line vs. accelerated depreciation: how the same asset gets charged differently to the income statement — and why the choice quietly reshapes reported earnings for years. Libby's Chapter 8 and AMS Chapter 11 trace every method with full numerical examples, including how gains and losses arise when assets are sold or retired.
When a company buys a long-lived asset — a factory, a fleet of trucks, a piece of manufacturing equipment — it doesn't expense the full cost in the year of purchase. Instead, the cost is spread across the asset's useful life through annual depreciation charges. This is the matching principle in action: match the cost of the asset to the revenue it helps generate, period by period.
But 'useful life' and 'how fast to spread the cost' involve significant judgment. A company buying $10 million of equipment can make very different choices: expense $1 million per year for 10 years (straight-line), front-load expenses heavily in year one and two (accelerated), or tie depreciation to actual production output (units of production). Each method is GAAP-compliant. Each produces different income in every year of the asset's life.
The cash went out the door when the asset was purchased. Depreciation is the accounting charge that spreads that cash cost across future periods — no additional cash leaves the company when depreciation expense is recorded. This is why analysts add depreciation back when calculating EBITDA (Earnings Before Interest, Taxes, Depreciation, and Amortization) and why free cash flow often differs substantially from net income.
The simplest and most widely used method. Depreciation expense is identical in every year of the asset's life.
Straight-Line Depreciation
Annual Depreciation = (Cost − Salvage Value) ÷ Useful Life
Salvage value is the estimated residual value at end of useful life.
| Year | Book Value (Start) | Depreciation | Accumulated Depr. | Book Value (End) |
|---|---|---|---|---|
| 1 | $100,000 | $18,000 | $18,000 | $82,000 |
| 2 | $82,000 | $18,000 | $36,000 | $64,000 |
| 3 | $64,000 | $18,000 | $54,000 | $46,000 |
| 4 | $46,000 | $18,000 | $72,000 | $28,000 |
| 5 | $28,000 | $18,000 | $90,000 | $10,000 |
Annual depreciation = ($100,000 − $10,000) ÷ 5 = $18,000. The book value declines at a constant rate, reaching salvage value exactly at the end of year 5. Most companies use straight-line for financial reporting because it produces smoother, more predictable earnings.
Accelerated methods charge more depreciation in early years and less in later years. The economic rationale: assets often generate more value (and wear out faster) in their early life. The practical rationale for taxes: front-loading deductions reduces taxable income now, deferring tax payments to the future.
Double declining balance (DDB) is the most common accelerated method. The rate is double the straight-line rate, applied to the declining book value each year — not the original cost.
Double Declining Balance
Annual Depreciation = (2 ÷ Useful Life) × Beginning Book Value
Salvage value is not subtracted from cost upfront — but book value cannot fall below salvage value.
| Year | Book Value (Start) | DDB Rate | Depreciation | Book Value (End) |
|---|---|---|---|---|
| 1 | $100,000 | 40% | $40,000 | $60,000 |
| 2 | $60,000 | 40% | $24,000 | $36,000 |
| 3 | $36,000 | 40% | $14,400 | $21,600 |
| 4 | $21,600 | 40% | $8,640 | $12,960 |
| 5 | $12,960 | — | $2,960* | $10,000 |
In year 5, the full DDB rate would give $5,184 — but that would reduce book value below the $10,000 salvage value. So depreciation is capped at $2,960 (enough to reach exactly $10,000). Total depreciation under both methods is identical over the asset's full life: $90,000. The difference is purely timing.
Notice the critical difference: DDB charges $40,000 in year 1 vs. $18,000 under straight-line. A company choosing DDB reports $22,000 less pre-tax income in year 1 — and correspondingly more income in years 4 and 5. For tax purposes, this deferral is valuable: paying $22,000 less tax today (using the money for operations) and more tax later is economically beneficial.
Book Value Over Time — Straight-Line vs Double Declining Balance
Example: $100,000 asset · $10,000 salvage value · 5-year life
Start
Year 1
Year 2
Year 3
Year 4
Year 5
↑ $10K salvage floor — neither method goes below
Straight-Line — Smoother earnings
Equal $18,000 expense every year. Predictable, easy to explain, preferred for financial reporting.
$18K
$18K
$18K
$18K
$18K
DDB — Front-loaded expense
Heavy early, light late. Tax benefit: deduct more now, pay less tax today. Common for MACRS tax depreciation.
$40K
$24K
$14.4K
$8.6K
$3K
Total depreciation over 5 years is identical under both methods: $90,000 (cost $100K − salvage $10K). The difference is only timing.
Figure 2.1 — DDB front-loads $40K of depreciation in Year 1 vs SL's $18K — a $22K difference in reported pre-tax income. The totals equalize by Year 5. Most companies use SL for reporting and DDB for taxes.
Units of production ties depreciation to actual usage rather than time. If a machine is expected to produce 500,000 units over its life, each unit produced 'uses up' a proportionate share of the machine's cost.
Units of Production Rate
Depreciation/Unit = (Cost − Salvage Value) ÷ Total Expected Units
Annual depreciation = Depreciation/Unit × Units Produced That Year
This method produces highly variable depreciation expense that moves with production volume — low in slow years, high in busy ones. It's most appropriate for assets whose wear is driven by use (mining equipment, printing presses, aircraft engines measured in flight cycles) rather than the passage of time.
Most large companies maintain two depreciation schedules simultaneously: one using straight-line for GAAP financial reporting (smoother earnings, simpler investor communication) and one using MACRS (Modified Accelerated Cost Recovery System) for tax returns (front-loaded deductions to defer tax payments). This is completely legal, common, and disclosed in the footnotes.
In early years, tax depreciation exceeds book depreciation — so the company pays less tax than its GAAP income would suggest. The taxes deferred to future years accumulate as a Deferred Tax Liability (DTL) on the balance sheet. In later years, the pattern reverses and the DTL is paid down. For growing companies that continuously add assets, the DTL grows indefinitely — effectively an interest-free loan from the government.
Asset: $100K cost, 5-year life, no salvage. Book depreciation (straight-line): $20K/year. Tax depreciation (MACRS year 1): $40K. Taxable income is $20K lower than book income in Year 1. At a 25% tax rate: taxes actually paid are $5K lower than the GAAP provision. This $5K is booked as a Deferred Tax Liability — the company will owe it in Years 4 and 5 when tax depreciation falls below book depreciation. Large industrials like GE, Boeing, and Caterpillar carry hundreds of millions in DTLs from cumulative depreciation differences.
On the balance sheet, PP&E is typically shown at original cost with accumulated depreciation subtracted to arrive at net book value. The relationship between these two figures is a quick signal of asset age.
A company shows PP&E at cost of $800M and accumulated depreciation of $680M — net book value of $120M. The asset base is 85% depreciated ($680M / $800M). In most industries this signals an aging asset base that will soon require significant capital expenditure to replace. Compare to a competitor with PP&E at cost of $900M and accumulated depreciation of $200M (22% depreciated) — that company has relatively new assets and faces lower near-term reinvestment pressure.
Most companies use straight-line for financial reporting (smoother earnings, simpler explanation to investors) and accelerated methods (MACRS — Modified Accelerated Cost Recovery System) for tax purposes. This creates deferred tax liabilities on the balance sheet — the tax the company will eventually owe when depreciation reverses. It's entirely legal and extremely common. The gap between book depreciation and tax depreciation can represent hundreds of millions of dollars at large industrials.
Key Takeaways
A company purchases equipment for $60,000 with a $6,000 salvage value and a 6-year useful life. What is annual straight-line depreciation?