Be aware the only the calculations shown in Part III of the worksheet are incorrect, but TurboTax doesn't actually seem to use the calculations on Part III for anything. TurboTax appears to use the same calculation method, but done separately, to determine the allowable contribution. You can enter $20,500 on line 6a of Part I or mark the Maximize box on line 6d and TurboTax will properly calculate the maximum permissible deduction despite the erroneous calculation shown in Part III.
