I've also been going crazy with the "depreciation adjustment," which increases AGI on the MA return. It has nothing to do with the Sec 179 or bonus depreciation taken on the federal return. I just printed (to .pdf) the ALL FORMS AND WORKSHEETS package, and the last page of the federal documents is a Schedule E Worksheet (for a rental property I have) that shows "non-conformity" between how depreciation is calculated on Cars and Trucks for Federal purposes versus how it is calculated for MA. The depreciation for MA is much less. After further digging on Mass.gov, the only reference to this I found was on a webpage entitled "TIR 03-25: Depreciable Business Assets; Modifications For Decoupling From Federal Bonus Depreciation," which was last updated in 2004. According to the webpage, it would appear that MA uses REV. PROC. 2003-75 TABLE 1 as the limitations for passenger vehicles... it's a 2003 table that hasn't been (and doesn't get) adjusted for inflation. It seems wonky to me, but after recalculating the MA depreciation myself using the 2003 limits in Table 1 for a vehicle put into service in 2020, I was able to calculate the depreciation adjustment for the last few years. That explains why my depreciation expense for MA has been significantly lower than the Federal amount every year. Whether it's right or wrong, I don't know!
