Since your MAGI is determined by taking your AGI and “adding back” certain deductions, it would be your net capital gain that enters into the computation as that is what is included in your AGI. (Limited of course to the $3,000. net capital loss which is the maximum net capital that would be includible in your AGI if your capital losses exceed your capital gains).
These are items which can be subtracted from your AGI, but must be included in the calculation of your MAGI:
• ½ of self-employment tax (self-employed individuals are required to pay “payroll” taxes that an employer would otherwise take; these extra taxes can be deducted from AGI, but are included in MAGI)• Student loan interest• Tuition and fees deduction• Qualified tuition expenses• Passive income or loss (from Schedule E)• Rental losses• IRA contributions and taxable Social Security payments• Exclusion for income from U.S. savings bonds• Exclusion for adoption expenses (under 137)
Most of the above deductions are rare, so don’t be surprised if your AGI and your MAGI are the same.