Mar 19, 2018 The Tax Cuts and Jobs Act significantly changed bonus depreciation in 2018 Under the new law, the bonus depreciation rates are as follows:. Feb 1, 2020 The TCJA increased the additional first-year depreciation deduction in Sec. 28, 2017, and that was placed in service before Jan. 1, 2020. for 100% bonus depreciation rather than the reduced bonus depreciation rate. Learn the definition of depreciation, how is it calculated, and how it affects Updated January 28, 2020 This number is then divided over the years of " useful life" of the asset.4 Useful life is determined by the IRS based on a schedule set up