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In looking at the schedule you provided, it seems like your preparer used "Actual Expenses" and included the Truck as an asset subject to depreciation.  You should be able to find the depreciation expense from the 4562 flowing to a line on your business schedule (C, or E, or F, etc.) for 2019 and 2020.  You can't claim both depreciation (part of actual expenses) and Standard Mileage. FM or 'full-month' convention is a common convention used for financial reporting (book depreciation) versus tax depreciation. Because the asset was placed in service in July, using a Half-Year convention with SL method (if done correctly) would have resulted in the same depreciation expense calculation (6 full months) as using FM with SL method. The correct calculation of the truck using FM (or HY since placed-in-service 7/1/2019) and SL is attached. See the Calculated Depr line for the correct calculation - literally the cost divided by 60 months with 6 months claimed in the first and last years. The Reported Depr line is what your preparer reported for 2019 and 2020. The Adjustment is the difference. If you enter the accumulated depr into TT as of 2020, then TT will pro-rate the adjustment amount over the remaining 4 years of 2021-2024 resulting in the Reported Depr amounts. The calculation for the Laser 3D Pro, is calculated correctly, so I do not believe any calculation for short years or mid-quarter convention has been applied by your preparer. I provide tax depr guidance to clients as part of my occupation. I would enter it into TT and use the Reported Depr for 2021-2024 in order to claim all of the Depreciation over the life of the asset.