Just clarifying based on the IRS publication here:
https://www.irs.gov/publications/p590a#en_US_2018_publink[phone number removed]
That capital losses do NOT factor into the calculation of MAGI for the purposes of figuring out IRA contribution amounts that are allowed.
On that page they have a section "Worksheet 1-1. Figuring Your Modified AGI"
And in that calculation no where does it mention capital losses.
Many websites around the web do say that you use capital losses to calculate MAGI for the purposes of IRA contributions but I'm just clarifying that I should go by the IRS publication and not random websites.