I have a similar depreciation "math error" from 2015 that I just discovered for 2020. I changed my property from personal use to rental property 9/1/2014 which 2014 return calculated Business Use 33.3%. TT has continued the Depreciable Basis calculation at the Business Use 33.3% through 2019 return. I don't want to go through the amended return process unless it would result in significant refunds. Am I correct that I could only amend the past 3 of 5 years returns anyway? Can I on the 2020 return just indicate the actual prior depreciation taken (at the 33/3% rate), change Business Use to 100% which updates the Depreciable Basis, and start using the new updated rate of depreciation on the Depreciated Basis for the remainder of the 27.5 years? The difference in Depreciable Basis: $40,135 (33/3%) & $85,525 (100%).
