Calculating the cost of your equipment after the Section 179 deduction is simple. All you need to know is your first-year write-off, first-year bonus depreciation, and normal first-year depreciation. You then add these three amounts together to find your total first-year deduction. You also need to calculate your cash savings, which you can find by taking the total cost of your equipment purchases and multiplying that number by your local tax rate. Subtract your cash savings from the total first-year deduction to find the cost of your equipment after-tax.