What straight-line depreciation is and why you need it

Straight-line depreciation is a method of spreading the cost of an asset evenly across the years you own it. You take the purchase price, subtract what it will be worth at the end of its useful life, divide by the number of years you plan to use it, and that number is your annual depreciation expense. It is the simplest depreciation method and the one most small business owners and property managers use.

You need this calculation if you own a business, rental property, or significant equipment. It affects your tax deductions, your financial statements, and how much profit you report to the IRS. The IRS does not require you to use straight-line depreciation for everything—some assets have rules about which method you must use—but for most business property and rental buildings, you have the choice, and straight-line is the easiest to track and defend in an audit.

Key Takeaways

  • The straight-line formula is (Asset Cost − Salvage Value) ÷ Useful Life in Years = Annual Depreciation.
  • You must know three numbers: what you paid for the asset, what it will be worth when you stop using it, and how many years you plan to use it.
  • The IRS publishes useful life ranges for different asset types in Publication 946, and you must stay within those ranges or your deduction may be challenged.
  • Depreciation is a non-cash expense that reduces your taxable income each year, even though you are not spending money that year.
  • You record depreciation on a balance sheet and in a depreciation schedule, and you track it in an accumulated depreciation account.

The three numbers you need to gather

Before you can calculate anything, you need the purchase price of the asset, the salvage value, and the useful life. The purchase price is straightforward—it is what you actually paid, including shipping, installation, and any other costs to get it ready to use. Do not use the list price or the price you negotiated down from; use the real amount that left your account.

Salvage value is what you expect the asset to be worth when you are done with it. For a vehicle, this might be the scrap or resale value. For a building, it is often the land value alone, since the building itself may be worthless by then. For equipment, it might be zero. If you have no idea, zero is a safe assumption and is what most small business owners use. The IRS does not require you to guess accurately here—you just need a reasonable estimate that you can defend.

The useful life is how many years you plan to use the asset for business or income purposes. This is not how long the asset will physically last; it is how long you intend to own it and use it. The IRS publishes ranges for different types of property in Publication 946: How to Depreciate Property. Office furniture is typically 7 years, vehicles are 5 years, and residential rental buildings are 27.5 years. Commercial buildings are 39 years. You must stay within the IRS ranges or your deduction can be disallowed.

The straight-line depreciation formula and a worked example

The formula is straightforward:

(Asset Cost − Salvage Value) ÷ Useful Life in Years = Annual Depreciation Expense

Here is a real example. You buy a delivery van for your business for $35,000. You expect it to be worth $5,000 when you sell it in five years. The IRS says vehicles are 5-year property.

($35,000 − $5,000) ÷ 5 = $6,000 per year. Every year for five years, you deduct $6,000 from your business income as a depreciation expense. At the end of five years, you will have deducted $30,000 total, and the van will be fully depreciated on your books (even if you still own it or it is still worth something).

Another example: You buy a rental house for $250,000. The land is worth $50,000 and the building is worth $200,000. You can only depreciate the building, not the land. The useful life for residential rental property is 27.5 years.

($200,000 − $0) ÷ 27.5 = $7,272.73 per year. You deduct this amount every year for 27.5 years. After that, the building is fully depreciated and you stop taking the deduction, even if you still own the property.

How to record depreciation on your books

You track depreciation in two places: on your balance sheet and in a depreciation schedule. On the balance sheet, the asset appears at its original cost, and below it you list accumulated depreciation—the total amount you have deducted so far. The difference between the two is the book value of the asset.

For the van example, after year one your balance sheet shows: Van $35,000, Accumulated Depreciation ($6,000), Book Value $29,000. After year two: Van $35,000, Accumulated Depreciation ($12,000), Book Value $23,000. And so on.

You also keep a depreciation schedule—a straightforward table or spreadsheet that lists each asset, its cost, salvage value, useful life, annual depreciation, and the accumulated depreciation for each year. This is what you show the IRS if you are audited. Many accounting software programs (QuickBooks, Xero, Wave) can generate this automatically once you enter the asset details.

When the IRS requires different depreciation methods

Straight-line is optional for most business property, but not all. Section 1245 property—equipment, machinery, vehicles, and furniture—can use straight-line or accelerated methods like MACRS (Modified Accelerated Cost Recovery System). Section 1250 property—buildings and structures—must use straight-line under current tax law, so you have no choice there.

If you buy used property, the same rules explore; the useful life does not change based on the asset's age. If you buy a five-year-old vehicle, it is still 5-year property, and you still depreciate it over five years from the date you bought it.

There are also special rules for property you buy and place in service partway through the year. The IRS uses a half-year convention for most property, meaning you deduct half a year's depreciation in the year you buy it, regardless of the month. So if you buy the van in November, you still deduct $3,000 (half of $6,000) that year, and then $6,000 for the next four full years, and $3,000 in year six.

Common mistakes to avoid

The most common mistake is using the wrong useful life. Check Publication 946 before you start. If you guess and the IRS disagrees, you will owe back taxes plus interest and possibly penalties. Another mistake is depreciating land. Land does not wear out, so it is never depreciable. If you buy a property, you must separate the land value from the building value and depreciate only the building.

A third mistake is forgetting to track accumulated depreciation. If you sell the asset before it is fully depreciated, you need to know how much you have deducted so far, because the difference between the sale price and the book value is a gain or loss that affects your taxes. If you have no record, the IRS will assume you deducted nothing, and you will owe tax on the full sale price.

Finally, do not depreciate personal property. If you use an asset partly for business and partly for personal use, you can only depreciate the business-use portion. A home office desk is depreciable; your personal dining table is not, even if you sometimes work at it.

Frequently Asked Questions

Can I change my depreciation method after I have already started depreciating an asset?

You can, but it requires IRS permission. You file Form 3115 (process for Change in Accounting Method) and usually pay a user fee. For most small business owners, it is not worth the hassle. Choose your method carefully the first year and stick with it.

What happens to depreciation when I sell the asset?

You stop depreciating it the year you sell it. You calculate your gain or loss by subtracting the book value (original cost minus accumulated depreciation) from the sale price. If you sell the van for $8,000 after three years, and you have deducted $18,000 in depreciation, the book value is $17,000, so your gain is $8,000 − $17,000 = a loss of $9,000.

Do I have to depreciate an asset, or can I deduct the whole cost in year one?

For most assets, you must depreciate over time. However, the IRS allows Section 179 expensing for certain property, which lets you deduct the full cost in the year you buy it, up to an annual limit. There are also bonus depreciation rules that change yearly. Talk to a tax professional to see if either applies to your situation.

Is depreciation the same for tax purposes and financial reporting?

Not always. For tax purposes, you follow IRS rules and useful lives. For financial reporting (if you prepare statements for a bank or investor), you might use different useful lives based on how long you actually plan to use the asset. Most small businesses use the same method for both to keep things straightforward.

What if I use an asset for both business and personal reasons?

You depreciate only the business-use percentage. If you use a vehicle 70 percent for business and 30 percent for personal use, you depreciate only 70 percent of the cost. You must track this split carefully, because the IRS will challenge it if your records are weak.