Structure Each year's worth of depreciation should be deductible from that year's gross income Difficult to measure true depreciation, or even the useful life of durable goods. Instead, the tax law specifies a tax life For each asset, what proportion of its acquisition value can be depreciated each year, and over how many years.9 Structure • Each year’s worth of depreciation should be deductible from that year’s gross income. • Difficult to measure true depreciation, or even the useful life of durable goods. Instead, the tax law specifies a tax life: – For each asset, what proportion of its acquisition value can be depreciated each year, and over how many years