SteamTrain is correct, tax exempt income is not added to AGI when calculating the MAGI for the purpose of a Roth IRA contribution. SteamTrain provided the link to the worksheet for calculation the MAGI for the purpose of a Roth IRA contribution.
The MAGI from Healthcare.gov is for the purpose of determining Premium Tax Credits and has nothing to do with Roth IRA contributions. There are dozens of different ways to modify AGI for different purposes.
