Understand the concept of straight-line depreciation: It is a method used to allocate the cost of an asset evenly over its useful life. The formula involves subtracting the salvage value (the estimated residual value of the asset at the end of its useful life) from the cost of the asset and dividing the result by the useful life of the asset.
Identify the components of the formula: The formula for straight-line depreciation is \( \text{(Cost} - \text{Salvage Value)} \div \text{Useful Life} \). Here, 'Cost' refers to the initial purchase price of the asset, 'Salvage Value' is the expected value of the asset at the end of its useful life, and 'Useful Life' is the estimated time period the asset will be used.
Compare the given options: Evaluate each option provided in the problem. The first option \( \text{Cost} \times \text{Depreciation Rate} \) is incorrect because it does not account for salvage value or useful life. The second option \( \text{(Cost} - \text{Salvage Value)} \div \text{Useful Life} \) matches the correct formula for straight-line depreciation. The third option \( \text{(Cost} + \text{Salvage Value)} \div \text{Useful Life} \) is incorrect because it adds salvage value instead of subtracting it. The fourth option \( \text{Book Value} \times \text{Depreciation Rate} \) is incorrect as it represents a different depreciation method (e.g., declining balance).
Explain why the correct formula works: Subtracting the salvage value ensures that only the depreciable amount of the asset is allocated over its useful life. Dividing by the useful life ensures the depreciation expense is spread evenly across each accounting period.
Conclude with the correct formula: The correct formula for calculating straight-line depreciation is \( \text{(Cost} - \text{Salvage Value)} \div \text{Useful Life} \). This formula ensures accurate and consistent allocation of the asset's cost over its useful life.