The Straight Line Method (SLM) allocates the depreciable cost of a fixed asset equally over its estimated useful life. The same amount of depreciation is charged in every accounting period until the book value of the asset reaches its residual or salvage value. The method is simple and provides a systematic allocation of asset cost. However, it may not properly represent assets whose use, productivity, or reduction in value is not uniform throughout their useful lives.
Advantages of Straight Line Method
Simple and Easy to Calculate
The main advantage of the Straight Line Method is its simplicity. Annual depreciation can be calculated easily by deducting the residual value from the cost of the fixed asset and dividing the depreciable amount by the estimated useful life of the asset.
Once the cost, residual value, and useful life are determined, the depreciation amount remains the same every year. Therefore, repeated complex calculations are generally not required.
Equal Depreciation Every Year
Under the Straight Line Method, an equal amount of depreciation is charged every year throughout the useful life of the asset. This provides consistency in the recognition of depreciation expense.
For example, if annual depreciation is calculated at ₹20,000, the business will normally charge ₹20,000 as depreciation in each year of the asset’s useful life. This makes the depreciation expense predictable and easy to understand.
Systematic Allocation of Asset Cost
The Straight Line Method provides a rational and systematic allocation of the depreciable cost of an asset over its useful life.
A long-term asset provides economic benefits to the business for several accounting periods. Instead of charging the entire cost of the asset in one year, the depreciable cost is equally allocated to the periods in which the asset is expected to be used.
Thus, the method supports the accounting concept of allocating asset cost to the accounting periods benefiting from its use.
Suitable for Time-Based Depreciation
The Straight Line Method is suitable where depreciation is based mainly on the passage of time. It assumes that the depreciable cost of the asset should be allocated equally over its estimated useful life.
Therefore, the method is useful where an equal allocation of asset cost over different accounting periods is considered appropriate.
Easy Determination of Book Value
The book value of an asset can be easily determined under the Straight Line Method. The book value is calculated by deducting accumulated depreciation from the original cost of the asset.
Book Value = Original Cost − Accumulated Depreciation
Since the annual depreciation amount remains constant, accumulated depreciation and the remaining book value of the asset can be calculated easily for each accounting year.
Asset is Depreciated up to Residual Value
Under the Straight Line Method, depreciation continues until the book value of the asset becomes equal to its estimated residual or salvage value.
The method therefore provides a clear depreciation schedule from the original cost of the asset to its expected residual value over the estimated useful life.
Disadvantages of Straight Line Method
Assumes Equal Allocation throughout Useful Life
The Straight Line Method assumes that an equal amount of asset cost should be allocated to every accounting period.
However, the actual use or economic benefit obtained from an asset may not always remain equal throughout its useful life. Some assets may be used more heavily in certain periods and less heavily in other periods.
In such cases, charging the same amount of depreciation every year may not represent the actual level of use of the asset.
Does Not Consider Actual Level of Activity
The Straight Line Method is mainly based on the passage of time and does not calculate depreciation according to the actual activity or use of the asset.
For example, a machine may produce a higher number of units in one year and fewer units in another year. Under the Straight Line Method, the same depreciation expense will generally be charged in both years.
In contrast, an activity-based or Units-of-Production Method calculates greater depreciation in years when the asset is heavily used.
May Not Reflect Accelerated Reduction in Asset Value
Certain assets may lose a larger portion of their value during the earlier years of their useful lives. The Straight Line Method does not provide accelerated depreciation because the same amount is charged every year.
For assets whose value decreases more rapidly during the initial years, a Declining Balance or Double-Declining-Balance Method may better represent the pattern of depreciation.
Does Not Consider Changes in Productivity
The Straight Line Method does not directly consider changes in the productivity of an asset.
Some assets may be more productive when they are new and their productivity may decrease as they become older. The Sum-of-Years-Digits Method is based on this assumption and charges higher depreciation in earlier years.
The Straight Line Method, however, continues to charge the same depreciation amount even when the productivity of the asset changes.
Depends on Estimates
Calculation of depreciation under the Straight Line Method depends on the estimated useful life and expected residual or salvage value of the asset.
If these estimates do not properly represent the expected useful period or residual value of the asset, the annual depreciation amount calculated under the method may also be affected.
Therefore, the depreciation calculation is dependent on the estimates used for the asset.
May Not Match Cost with Actual Asset Use
Depreciation is intended to allocate asset cost to the periods in which the organisation receives benefits from the use of the asset. Where the level of asset use varies significantly from year to year, equal depreciation may not closely match the cost allocation with the actual level of asset use.
For such assets, an activity-based method may provide depreciation based on actual miles driven, machine cycles, or units produced.
Exam Focus
The main advantages of the Straight Line Method are simplicity, easy calculation, equal annual depreciation, systematic allocation of asset cost, and easy determination of book value.
The method is mainly suitable where depreciation is based on the passage of time and an equal allocation of depreciable cost over the useful life is appropriate.
The major limitation of the Straight Line Method is that it charges equal depreciation every year without considering actual asset use, changes in productivity, or a faster reduction in value during the earlier years.
For assets that are heavily used in certain periods, the Units-of-Production Method may better reflect actual activity. For assets that lose more value in their earlier years, an accelerated depreciation method such as the Declining Balance Method or Sum-of-Years-Digits Method may be more appropriate.