To calculate MAGI for Roth IRA contributions use Worksheet 2-1 in IRS Publication 590-A. It doesn't say anything about adding back rental losses. (There's a note at the bottom of the worksheet, that I don't quite understand, about refiguring your AGI in certain cases if you have passive activity losses. But you said you are active.)
Worksheet 2-1 (online)
Publication 590-A (download PDF)
You didn't say what specific Intuit article you looked at. I know there's one that talks about MAGI in general terms. It describes one way of calculating MAGI, but doesn't point out that there are different definitions of MAGI for different purposes. From the article you would think that MAGI is always calculated the same way, for all purposes.
