Straight-line depreciation

Straight-line depreciation is the simplest and most common method of depreciation. It allocates the cost of an asset equally across each year of its useful life. If an asset costs $100,000 and has a 10-year life with zero salvage value, straight-line depreciation is $10,000 per year. There is no acceleration or deceleration of the expense. Straight-line depreciation is the default choice for most companies under both GAAP and IFRS, because it is simple, transparent, and matches many assets’ actual decline in value.

The formula and mechanics

Straight-line depreciation is calculated as:

Annual depreciation = (Asset cost - Salvage value) ÷ Useful life in years

Example: A building costs $5,000,000 with an estimated 40-year life and zero salvage value. Annual depreciation = $5,000,000 ÷ 40 = $125,000 per year

The same $125,000 is recorded as depreciation expense in year 1, year 2, and every year through year 40.

Advantages of straight-line method

Simplicity: It requires no complex calculations or assumptions beyond the initial useful-life estimate.

Transparency: Anyone reading the financials can easily verify the depreciation expense and understand how it was calculated.

Stability: Profit is not distorted by accelerated early charges. Depreciation is constant, making profit more predictable and comparable across years.

Consistency with economic reality: For many assets (buildings, office furniture), value declines relatively evenly over time. Straight-line depreciation reflects this reality.

Default choice: Most companies use straight-line depreciation for this reason, which makes financial statements more comparable.

Suitable asset types

Straight-line depreciation is appropriate for:

• Buildings and structures (which decline in value relatively evenly).
• Office equipment and furniture.
• Long-term leasehold improvements.
• Infrastructure and utilities.

It is less suitable for:

• Vehicles and equipment subject to technological obsolescence (which decline faster early).
• Assets whose productive capacity declines with use (declining-balance-depreciation or units-of-production-depreciation may be better).

Comparison to other methods

Declining-balance depreciation: Recognizes larger expense early (reflecting faster value loss), smaller later. Total expense is the same, but the timing differs.

Units-of-production depreciation: Expense is based on actual usage. A vehicle might be depreciated per mile; production equipment per unit output.

For income statement comparability, straight-line depreciation is preferred because it eliminates variability from the depreciation component.

Tax vs. book depreciation

For book (financial reporting) purposes, US companies typically use straight-line depreciation. For tax purposes, the IRS requires MACRS (Modified Accelerated Cost Recovery System), which typically accelerates depreciation.

This difference creates deferred-tax-liability and deferred-tax-asset. The company might record $100,000 of straight-line book depreciation but $120,000 of accelerated tax depreciation.

Useful life estimation

The critical judgment in straight-line depreciation is estimating useful life. A company might estimate a building’s life at 40 years, equipment at 7 years, or vehicles at 5 years. These estimates are disclosed in footnotes.

If a company changes its useful-life estimate (e.g., deciding equipment will last 10 years instead of 7), the change must be disclosed and is applied prospectively (not to prior years).

See also