i sympathized with you because MAGI can differ depending on what tax issue is being considered. so for what purpose are you trying to compute MAGI
se health insurance is not dependent on MAGI
it's limited to net self-employment income reduced by contributions to self-employment retirement plans and 1/2 of the SE tax. as you can see this has no relation to AGI or MAGI. other limitations may apply if you are eligible to participate in any subsidized health plan maintained by any employer (other than yourself) of you, your spouse, your dependents or any child under 27. it can be even more complicated if you had Obamacare
for the taxable portion of social security use the worksheet on page 31 of the 1040 instructions
Exception. Do not use the Social Security Benefits Worksheet in these instructions if any of the following applies.
• You made contributions to a traditional
IRA for 2021 and you or your
spouse were covered by a retirement
plan at work or through self-employment.
Instead, use the worksheets in
Pub. 590-A to see if any of your social
security benefits are taxable and to figure
your IRA deduction.
• You repaid any benefits in 2021
and your total repayments (box 4) were
more than your total benefits for 2021
(box 3). None of your benefits are taxable
for 2021. Also, if your total repayments
in 2021 exceed your total benefits
received in 2021 by more than $3,000,
you may be able to take an itemized deduction
or a credit for part of the excess
repayments if they were for benefits you
included in income in an earlier year.
For more details, see Pub. 915.
• You file Form 2555, 4563, or
8815, or you exclude employer-provided
adoption benefits or income from sources
within Puerto Rico. Instead, use the worksheet in Pub. 915.
https://www.irs.gov/pub/irs-pdf/i1040gi.pdf
