The half-year convention for depreciation is an accounting concept that allows companies to spread out their expenses in both the first and last years of owning an asset. This typically results in expensing half of the total expected annual depreciation each year of the asset's life. The purpose of the half-year convention is related to the matching principle, which states expenses should match up with the revenues generated by the expense in the same accounting period.

The concept of the half-year convention can be applied to all types of depreciation methods, such as straight-line, double declining balance, or sum-of-the-years' digits. For example, if a company purchases an asset for $10,000 and plans to depreciate the asset by $3,000 over its useful life of three years under the straight-line method, the company would use the half-year convention to expense $1,500 of depreciation each year. The company would expense $1,500 in the first year, $1,500 in the second year, and $1,500 in the third year, for a total of $4,500 in depreciation expenses.

The half-year convention helps companies more accurately match expenses to the revenues generated by the asset, creating a better overall picture of the company's performance. By spreading out depreciation expenses evenly over an asset's useful life, the results of the matching principle are more likely to be achieved and the company's financial statements more accurately reflect the current value of an asset.

The half-year convention for depreciation is an important concept for businesses to understand and utilize when depreciating the cost of their assets. By spreading out depreciation expenses over an asset's useful life, companies can more accurately match expenses with revenues and provide a better indication of their financial performance.