The straight line method is the simplest way to depreciate an asset, spreading its cost evenly across every year of its useful life. If you buy a piece of equipment for $50,000 and expect it to last ten years, you expense the same amount each year until the asset is fully depreciated. It’s the most widely used depreciation method in financial accounting and the default choice for many types of property on tax returns as well.
The Formula and How It Works
Straight line depreciation uses three numbers: what you paid for the asset, what it will be worth when you’re done with it, and how many years you plan to use it.
Annual Depreciation = (Purchase Price − Salvage Value) ÷ Useful Life
The purchase price is your total cost to acquire the asset, including shipping, installation, or any other expense needed to put it into service. Salvage value is what you estimate the asset will be worth at the end of its useful life, sometimes called residual value. The gap between those two numbers is the depreciable base, the total amount you’ll write off over the asset’s lifetime. Useful life is the number of years you expect the asset to remain productive.
Say you buy a delivery van for $40,000. You expect to use it for five years and then sell it for $5,000. Your depreciable base is $35,000, and your annual depreciation expense is $7,000. Every year for five years, you record exactly $7,000 in depreciation. That’s it.
A Worked Example
A small business buys office furniture for $12,000. The furniture has an estimated useful life of seven years and a salvage value of $500. The depreciable base is $11,500. Dividing by seven gives an annual depreciation expense of roughly $1,643. After seven years, the furniture sits on the books at $500, matching the estimated salvage value. If the business sells the furniture for more than $500 at that point, it records a gain. If it sells for less, it records a loss.
How to Record It on Your Books
Each year when you record straight line depreciation, you make a journal entry with two parts. You debit (increase) a depreciation expense account, which flows to your income statement and reduces your reported profit. You credit (increase) an accumulated depreciation account, which is a contra-asset on your balance sheet. That means it offsets the original cost of the asset, lowering the asset’s carrying value over time.
Using the delivery van example, you would debit depreciation expense for $7,000 and credit accumulated depreciation for $7,000 each year. After three years, accumulated depreciation totals $21,000, so the van’s book value is $19,000 ($40,000 minus $21,000). The original purchase price stays on the balance sheet; it’s the accumulated depreciation that grows until the asset is fully depreciated.
Why Businesses Choose This Method
The biggest draw is simplicity. The calculation takes about thirty seconds, and the same dollar amount repeats every year, making budgeting and forecasting straightforward. Because the expense is steady and predictable, it’s less prone to errors or misinterpretations in financial statements. Investors and lenders reviewing your books can see a consistent charge without needing to untangle changing depreciation rates.
Straight line depreciation also makes sense conceptually for assets that wear out at a roughly even pace. Office furniture, buildings, and leasehold improvements don’t typically lose most of their value in the first year. Spreading the cost evenly matches the expense to the revenue the asset helps generate over time, which is the core principle behind depreciation in the first place.
How It Differs From Accelerated Methods
Accelerated methods like double declining balance front-load depreciation, recording larger expenses in the early years and smaller ones later. A $40,000 van depreciated under the double declining balance method might show $16,000 in depreciation the first year instead of $7,000. That larger early write-off lowers taxable income faster, which is why many businesses prefer accelerated methods for tax purposes.
The trade-off is complexity and volatility. Accelerated methods can produce book values that dip below salvage value if you’re not careful, creating awkward adjustments when the asset is sold. They also make year-to-year profit comparisons harder because the depreciation charge changes every period. Straight line avoids both issues by keeping the math flat and predictable.
Straight Line Depreciation on Your Tax Return
For federal taxes, the IRS generally requires businesses to use the Modified Accelerated Cost Recovery System (MACRS), which applies declining-balance methods and predetermined recovery periods rather than your own useful-life estimates. So even if you use straight line depreciation on your financial statements, your tax depreciation may look different.
That said, several situations call for or allow the straight line method on your tax return:
- Intangible property: If you can depreciate intangible assets, you generally use the straight line method.
- Computer software: Depreciable software uses straight line depreciation over a useful life of 36 months.
- Electing straight line under MACRS: You can choose straight line over the standard MACRS recovery period for any property class by entering “S/L” on Form 4562. This might make sense if your business has low taxable income and doesn’t benefit from larger early deductions.
- Alternative Depreciation System (ADS): The IRS requires ADS, which uses the straight line method, for tax-exempt use property, tax-exempt bond-financed property, tangible property used predominantly outside the United States, and listed property (like vehicles) used 50% or less for business. Real property held by an electing real property trade or business also falls under ADS.
Once you elect ADS for a property class, you can never revoke that election. It applies to all property in that class placed in service during the same year, with one exception: residential rental and nonresidential real property can be elected on a property-by-property basis.
Choosing the Right Useful Life
For financial reporting, you estimate useful life based on how long you actually expect to use the asset. A laptop might have a useful life of three years even though it still powers on after five, because your business replaces laptops on a three-year cycle. A commercial building might have a useful life of 30 or 40 years.
For tax purposes, the IRS assigns recovery periods by asset class rather than letting you pick your own timeline. Vehicles and computers typically fall into a five-year recovery period, office furniture into seven years, and nonresidential real property into 39 years. These recovery periods apply under MACRS regardless of whether you use the accelerated or straight line method within that system. The difference between your book useful life and the IRS recovery period is one reason your financial-statement depreciation and your tax depreciation often produce different numbers for the same asset.
When Straight Line Is the Best Fit
If you’re a small business owner who wants clean, easy-to-understand financial statements, straight line depreciation is hard to beat. It works especially well for assets with long, steady service lives: buildings, furniture, fixtures, and improvements. It’s also the standard method for intangible assets like patents or purchased software.
For assets that lose value quickly in their early years, like vehicles, technology equipment, or specialized machinery, an accelerated method may better reflect reality on your financial statements and deliver bigger tax deductions upfront. Many businesses use straight line for book purposes and MACRS accelerated methods for tax purposes, then track the difference between the two as a deferred tax item on their balance sheet.