Why Depreciation Is an Adjustment
A business may pay for equipment when it acquires the asset, but the equipment can help generate revenue over several accounting periods. Recording the entire cost as an expense on the purchase date would not allocate that cost to the periods that use the asset. Depreciation provides a systematic way to allocate the asset’s depreciable amount over its estimated useful life.
Straight-line depreciation assigns an equal amount of depreciation expense to each full period in the asset’s useful life. The calculation uses three estimates or records: the asset’s cost, its estimated salvage value at the end of its useful life, and its useful life. In this tutorial, examples assume the asset is in service for the full accounting year. The calculation for an asset used for only part of a year is a separate issue.
Calculating Straight-Line Depreciation
Let \(C\) denote the asset’s cost, \(S\) its estimated salvage value at the end of its useful life, and \(n\) its useful life in years. The depreciable amount is \(C-S\). For a full year of straight-line depreciation, divide that amount by the useful life:
The cost is the amount recorded for the asset under the applicable accounting rules. Salvage value is an estimate, not an amount the business receives each year. It represents the expected value remaining at the end of the asset’s useful life. Useful life is the expected period the asset will be used to provide service; it need not equal the asset’s total physical life.
The formula assumes the cost, salvage value, and useful-life estimate are appropriate for the calculation, and that the period being recorded is a full year of depreciation under the stated assumptions. It does not calculate a partial-year amount or model a changing pattern of asset use. Straight-line depreciation is an allocation method: it does not measure the asset’s market value or imply that cash is being set aside.
Why the Formula Gives an Equal Annual Amount
The formula follows from two requirements of the straight-line method. First, only the portion of cost expected to be consumed during the useful life is allocated: the cost above estimated salvage value. Second, that total allocation is divided equally among the \(n\) full years.
The amount allocated over the asset’s useful life is \(C-S\), because \(S\) is the estimated amount remaining at the end rather than an amount to depreciate.
If each of \(n\) years receives the same depreciation amount \(D\), then \(nD=C-S\).
Dividing both sides by \(n\) gives \(D=(C-S)/n\). Therefore the same annual expense, \(D\), is recorded for each full year under the method’s assumptions.
This derivation also provides a useful check: multiplying annual depreciation by the useful life should recover the depreciable amount. If it does not, review the subtraction, division, and units.
Recording the Depreciation Adjustment
The periodic calculation becomes an adjusting journal entry. Depreciation expense is an expense account, so it is debited for the period’s depreciation. Accumulated depreciation is a contra-asset account associated with the depreciated asset; it normally has a credit balance and is credited when depreciation is recorded.
The debit to depreciation expense increases expenses for the period, reducing income, all else equal. The credit to accumulated depreciation records the cumulative allocation associated with the asset. It is not a liability and does not represent a separate cash fund. The asset’s original cost is not reduced by this entry; the adjustment is posted to the separate accumulated depreciation account.
When an accumulated depreciation balance already exists, the current-period expense is still calculated from the asset’s cost, salvage value, and useful life under the stated straight-line assumptions. The new entry is for the current period’s amount, not for the total accumulated amount. To find the new accumulated depreciation balance, add the current credit to the existing credit balance.
Worked Example: Calculating and Recording a Full Year
A hypothetical workshop buys a testing machine for $48,000. It estimates salvage value of $3,000 and a useful life of 9 years. The machine is in service for the full year, and there is no opening accumulated depreciation balance. Calculate and record the year’s straight-line depreciation.
Method. Find the depreciable amount, divide by the useful life, then record the resulting current-year amount with the depreciation adjusting entry. This method avoids treating the salvage estimate as an annual expense deduction.
Step 1: Depreciable amount. Subtract estimated salvage value from cost:
Step 2: Annual depreciation. Divide by 9 years:
Step 3: Adjusting entry. Debit Depreciation Expense for $5,000 and credit Accumulated Depreciation for $5,000. The account balances after this entry are a $5,000 debit in Depreciation Expense and a $5,000 credit in Accumulated Depreciation.
Check. The total planned allocation over 9 full years is \(9\times \$5{,}000=\$45{,}000\), equal to the depreciable amount. The entry’s debit and credit are both $5,000. The calculation and entry balance.
Reading the Existing Accumulated Depreciation Balance
Accumulated depreciation collects the depreciation amounts recorded over periods. To find the account balance after a new adjustment, use its opening balance and the current-period credit. Do not debit depreciation expense for the prior years again: those amounts have already been recognized in earlier periods.
Worked Example: Posting the Current Year After Earlier Adjustments
A hypothetical delivery company’s vehicle cost $31,200, has estimated salvage value of $1,200, and has a 5-year useful life. The vehicle is in service for the full current year. Before the current-year adjustment, Accumulated Depreciation has a $12,000 credit balance from earlier full-year entries. Calculate the current-year entry and the account balance afterward.
Method. Recalculate the annual straight-line amount from the asset estimates, then add only this year’s amount to the existing accumulated depreciation balance. This avoids recording the cumulative total as a new expense.
Step 1: Depreciable amount.
Step 2: Current-year depreciation.
Step 3: Record the current-year entry. Debit Depreciation Expense for $6,000 and credit Accumulated Depreciation for $6,000.
Step 4: Calculate the new accumulated balance. The opening credit balance is $12,000. Add this year’s $6,000 credit:
Check. The annual amount multiplied by the 5-year useful life is \(5\times \$6{,}000=\$30{,}000\), the depreciable amount. The current adjustment is $6,000, not $18,000; the $18,000 is the resulting accumulated balance. The journal entry’s debit and credit are equal.
Handling a Period-End Adjustment and Checking It
A period-end adjustment should answer two separate questions: how much depreciation belongs to the current period, and what is the accumulated balance after posting? The first amount is calculated from the straight-line formula. The second is obtained by adding the current-period credit to the opening accumulated depreciation balance.
A practical check sequence is:
- Confirm that cost, salvage value, and useful life are stated in compatible units.
- Subtract salvage value from cost to get the depreciable amount.
- Divide by the useful life to get depreciation for one full year.
- Record a debit to Depreciation Expense and an equal credit to Accumulated Depreciation.
- Compare total depreciation over the useful life with the depreciable amount.
For a full-year straight-line calculation, the cumulative allocated amount after \(k\) years is \(k(C-S)/n\), provided \(k\) is within the useful life and the estimates and method have not changed. This is a check on cumulative allocation; the adjusting entry for a particular year remains that year’s annual amount.
Worked Example: Checking a Later Full-Year Entry
A hypothetical firm has an inspection unit recorded at a cost of $76,500, an estimated salvage value of $4,500, and an 8-year useful life. It has been depreciated for 3 full years, giving an opening Accumulated Depreciation credit balance of $27,000. The unit is in service for the fourth full year. Find the current adjustment and check the accumulated balance after posting.
Method. Recompute the annual amount from the original estimates, record one year of expense, and reconcile the cumulative balance to four years of allocation. The common mistake avoided here is using the opening accumulated amount as the current-year expense.
Step 1: Depreciable amount.
Step 2: Annual depreciation.
Step 3: Current-year entry. Debit Depreciation Expense for $9,000 and credit Accumulated Depreciation for $9,000.
Step 4: New accumulated balance. Add the current credit to the opening credit:
Check. Four years of straight-line depreciation total \(4\times \$9{,}000=\$36{,}000\), which matches the post-entry accumulated balance. The total planned allocation for all 8 years is \(8\times \$9{,}000=\$72{,}000\), equal to cost less salvage value. The current-year expense is $9,000, not the $36,000 cumulative balance.
Common Mistakes and Exam Traps
The central calculation is simple, but exam problems can test whether the candidate distinguishes a period’s expense from estimates and balances associated with several periods.
- Depreciating the full cost. The straight-line numerator is cost less estimated salvage value, not cost alone.
- Recording the total accumulated amount as the current expense. The adjusting entry records this period’s depreciation. The accumulated balance includes prior periods.
- Crediting cash. Depreciation is an allocation entry, not a cash payment. The credit is to Accumulated Depreciation.
- Confusing useful life and salvage value. Useful life is a time period; salvage value is a dollar estimate.
- Changing the entry’s debit and credit. Depreciation Expense is debited; Accumulated Depreciation is credited.
For example, suppose cost is $60,000, salvage value is $6,000, and useful life is 9 years. The correct annual depreciation is \((\$60{,}000-\$6{,}000)\div 9=\$6{,}000\). A common wrong calculation is \(\$60{,}000\div 9=\$6{,}666.67\), which incorrectly allocates the salvage amount as depreciation. The correction is to subtract salvage value before dividing.
Check Your Understanding
For each problem, calculate the requested full-year depreciation and entry details. Assume the asset is in service for the full year and that no changes to estimates or method are stated.
- A hypothetical print shop buys a binding machine for $42,500, estimates salvage value of $2,500, and expects a 10-year useful life. Find annual depreciation and state the adjusting entry. (Answer: $4,000 annual depreciation; debit Depreciation Expense $4,000 and credit Accumulated Depreciation $4,000.)
- A hypothetical laboratory instrument costs $58,800, has estimated salvage value of $4,800, and a 9-year useful life. After two full years, what is the accumulated depreciation credit balance, assuming each year’s adjustment was recorded? (Answer: $6,000 annual depreciation; $12,000 accumulated depreciation credit balance.)
- A hypothetical service vehicle has cost $69,000, estimated salvage value $9,000, and useful life of 6 years. Its opening accumulated depreciation balance is a $30,000 credit. Find this year’s depreciation entry and the ending accumulated depreciation balance. (Answer: $10,000 current-year depreciation; debit Depreciation Expense $10,000 and credit Accumulated Depreciation $10,000; ending accumulated depreciation is a $40,000 credit.)
- A hypothetical data-storage system costs $95,000, has salvage value estimated at $5,000, and a 9-year useful life. An analyst proposes annual depreciation of $10,555.56 by dividing cost by life. Find the correct annual depreciation, identify the error, and give the first full-year entry. (Answer: $10,000 annual depreciation; the proposed method incorrectly depreciates the $5,000 salvage value; debit Depreciation Expense $10,000 and credit Accumulated Depreciation $10,000.)
- A hypothetical production press costs $84,000, has an estimated salvage value of $12,000, and a 12-year useful life. After 5 full years, the opening accumulated depreciation balance is $30,000 credit. Calculate the current-year expense and post-entry accumulated balance, then verify the cumulative amount against five years of allocation. (Answer: $6,000 current-year depreciation; $36,000 ending accumulated depreciation credit; five years of allocation are \(5\times \$6,000=\$30,000\) before the current year and \(6\times \$6,000=\$36,000\) after it.)