@JohnB5677 , that is not the correct method for calculating MAGI for the purpose of a Roth IRA contribution. See Worksheet 2-1 in IRS Pub 590-A for the correct calculation which TurboTax does on the Roth IRA Contribution Limit Worksheet:
https://www.irs.gov/pub/irs-pdf/p590a.pdf
TurboTax increasing the taxes due when a Roth IRA contribution is entered implies either having insufficient compensation to support the contribution or MAGI for the purpose of a Roth IRA contribution exceeding the threshold for the particular filing status.
