How to Calculate Depreciation on Fixed Assets
Depreciation allocates the depreciable amount of a tangible fixed asset over the periods that benefit from its use. It does not attempt to measure the asset’s current market value, and it does not create a fund of cash for replacement. The calculation begins with a properly determined asset cost, useful life, residual value, method, and date the asset is available for use.
Accounting depreciation and tax depreciation can differ substantially. Maintain separate book and tax schedules when required and apply the accounting framework, capitalization policy, and tax law relevant to the entity.
Quick Answer
For straight-line depreciation:
Annual depreciation = (asset cost − residual value) ÷ useful life
If equipment costs $50,000, has an estimated residual value of $5,000, and a five-year useful life, annual straight-line depreciation is $9,000. Adjust the first and final periods for the company’s convention and the date the asset becomes available for use.
Step 1: Confirm the Expenditure Is a Fixed Asset
A cost is generally capitalized when it creates a controlled resource expected to provide benefits beyond the current period and meets the accounting framework and company policy. Routine repairs and maintenance are usually expensed, while significant improvements may be capitalized.
Apply the capitalization threshold consistently. Do not split one asset into small invoices merely to avoid the policy.
Step 2: Determine the Asset’s Cost
Asset cost may include purchase price, nonrecoverable taxes, delivery, installation, testing, site preparation, professional fees, and other directly attributable amounts required to bring the asset to the location and condition necessary for use.
Exclude abnormal waste, general training, startup losses, and costs incurred after the asset is ready for use unless the framework requires otherwise.
Step 3: Identify the In-Service Date
Depreciation generally begins when the asset is available for its intended use, not necessarily when the invoice is paid or the asset first earns revenue. Document the date with installation, acceptance, commissioning, or operational records.
Step 4: Estimate Useful Life
Useful life is the period or production capacity over which the business expects to consume the asset’s benefits. Consider wear, expected usage, maintenance, shifts, technology, legal limits, lease terms, and replacement policy.
Tax life and manufacturer life are useful evidence but do not automatically determine book useful life.
Step 5: Estimate Residual Value
Residual value is the expected disposal proceeds at the end of useful life, net of disposal costs, based on the asset’s expected condition. Use zero when no meaningful residual value is supportable.
Review useful life and residual value periodically under the applicable framework. Changes are generally estimates applied prospectively rather than corrections of past depreciation.
Step 6: Choose the Depreciation Method
| Method | Best Fit |
|---|---|
| Straight line | Benefits consumed evenly over time |
| Declining balance | More benefit or obsolescence occurs early |
| Units of production | Consumption follows output or operating hours |
| Component depreciation | Significant parts have different useful lives |
The method should reflect the pattern of benefit consumption, not the method that creates the preferred profit.
Step 7: Calculate Straight-Line Depreciation
Suppose a vehicle costs $36,000, residual value is $6,000, and useful life is five years:
Depreciable amount = $36,000 − $6,000 = $30,000
Annual depreciation = $30,000 ÷ 5 = $6,000
Monthly depreciation is $500 when a monthly convention is used.
Step 8: Calculate Declining-Balance Depreciation
Under double-declining balance:
Rate = 2 ÷ useful life
For a five-year asset, the rate is 40%. Multiply the opening carrying amount by 40% each year, but do not depreciate the asset below residual value. Some policies switch to straight line when that produces a more appropriate remaining allocation.
Step 9: Calculate Units-of-Production Depreciation
Depreciation per unit = (cost − residual value) ÷ estimated total units
Period depreciation = rate per unit × actual period units
If a machine’s depreciable amount is $90,000 and expected output is 300,000 units, depreciation is $0.30 per unit. Production of 40,000 units creates $12,000 depreciation.
Step 10: Calculate Partial-Period Depreciation
Apply the company’s approved convention: exact days, full months, half-month, half-year, or another method permitted by the framework and policy. Use the same convention consistently and stop depreciation when the asset is derecognized or classified as required.
Step 11: Account for Significant Components
A building roof, aircraft engine, or major inspection may have a different useful life from the main asset. When required, recognize significant components separately and depreciate each over its own life.
When a component is replaced, derecognize the old component’s remaining carrying amount if identifiable.
Step 12: Record the Journal Entry
| Account | Debit | Credit |
|---|---|---|
| Depreciation expense | Period amount | — |
| Accumulated depreciation | — | Period amount |
Accumulated depreciation is a contra-asset account. The original asset cost normally remains visible until disposal.
Step 13: Update the Asset Register
Record asset identifier, description, location, custodian, cost, in-service date, method, life, residual value, current-period depreciation, accumulated depreciation, carrying amount, tax information, and disposal status.
Reconcile the asset register to the general ledger every reporting period.
Step 14: Review Impairment and Disposal
Depreciation does not replace impairment testing. If damage, obsolescence, poor performance, or market changes indicate that carrying value may not be recoverable, perform the applicable impairment review.
At disposal, remove asset cost and accumulated depreciation and recognize the difference between net proceeds and carrying amount as a gain or loss.
Worked Comparison
An asset costs $100,000, has no residual value, and a five-year life.
- Straight line: $20,000 each year.
- Double declining: Year 1 depreciation $40,000; Year 2 $24,000; later years decline, with final adjustment to avoid a negative carrying value.
- Units of production: Amount depends on actual output relative to estimated lifetime output.
Total depreciation over the asset’s depreciable life is the same depreciable amount; the timing differs.
Common Depreciation Mistakes
- Starting depreciation on the payment date instead of when available for use
- Including recoverable tax in asset cost
- Capitalizing routine repairs
- Using tax depreciation for book reporting automatically
- Ignoring residual value and components
- Depreciating land
- Continuing below residual value
- Failing to remove disposed assets
- Not reconciling the asset register to the ledger
Writer’s Opinion
The most important depreciation assumption is often useful life, not the formula. I would compare asset-register assumptions with actual replacement history, maintenance data, operating hours, and disposal proceeds. A standardized life table is useful, but it should not override strong evidence.
I also recommend separating book, tax, and management views. Combining them into one schedule creates confusion when their purposes and rules differ.
Video: Depreciation Explained
[youtube=https://www.youtube.com/watch?v=VhwZ9t2b3Zk]
Frequently Asked Questions
Does depreciation reduce cash?
No direct cash payment occurs when depreciation is recorded, although tax effects may influence cash.
Can an asset be fully depreciated and still used?
Yes. Continue tracking it in the asset register until disposal. Its continued use may indicate that useful-life estimates should be reviewed for similar assets.
Is land depreciated?
Land normally has an indefinite life and is not depreciated, although land improvements may be separate depreciable assets.
Can useful life be changed?
Yes when new information changes the estimate. Under many frameworks, the change is applied prospectively.
What is book value?
Carrying or book value is generally asset cost less accumulated depreciation and impairment, adjusted for other applicable measurement changes.
Final Checklist
- The expenditure meets capitalization requirements.
- Cost includes only appropriate directly attributable amounts.
- The in-service date is documented.
- Useful life, residual value, and method reflect expected use.
- Partial periods and components are handled consistently.
- The entry and asset register agree.
- Impairment, disposal, and tax differences are reviewed.
Correct depreciation begins with asset accounting, not a spreadsheet formula. Establish cost and use, choose a supportable pattern, update the register, and review assumptions throughout the asset’s life.
