UPDATE AS OF FEB. 24, 2018
The IRS is now accepting tax returns with the itemized deduction for PMI, and TurboTax has been updated to allow the deduction to be entered. After you enter the mortgage interest from box 1 of your Form 1098, the next screen has places to enter additional information from the 1098, including mortgage insurance premiums.
UPDATE AS OF FEB. 11, 2018
The answer below was correct when posted, on Jan. 27, 2018. However, the Budget Act that was passed and signed into law on Feb. 9 reinstates the deduction for mortgage insurance (PMI) for 2017. But it will be at least several weeks before the IRS revises the forms and its computer programs, and the revised forms can be incorporated in TurboTax. If you are itemizing deductions and you are eligible to deduct PMI, your simplest course of action would be to wait to file your tax return until TurboTax has been updated for the changes that were just instituted retroactively.
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Original answer posted January 27:
You don't enter PMI anywhere. The rule allowing PMI to be deducted expired at the end of 2016. The deduction is not available for 2017.
