The only MAGI worksheet in TurboTax is for the passive activity loss limitation for rental real estate on Form 8582. Is that the worksheet you are asking about? The IRS instructions for Form 8582 has a list of ten items that are not to be taken into account in calculating MAGI. One of those items is "The taxable amount of social security and tier 1 railroad retirement benefits." So social security income is not included in the MAGI worksheet in TurboTax because the IRS instructions specifically say to not include it.
There are about a dozen other definitions of MAGI for other purposes besides the passive activity loss limitation, but TurboTax does not have separate worksheets for those other MAGI calculations. Some of the other MAGI definitions include either the taxable amount of social security or total social security income.
