What lines of my w-2 are relevant to non-Massachusetts portion deductions?

[Zbucklyo]

MA provides a deduction for Medicare and Social Security taxes paid from income earned in MA, up to $2000.  If this is what you are referring to, and you earned income outside of MA, it is the amount of those taxes paid from noon MA employment.

If you only worked in MA, enter 0

[linear]

Sounds like you're trying to figure out the non-Massachusetts portion of deductions. It may not be as straightforward as looking at your W-2.

The "non-MA" portion is the part of your deductions that are attributed to non-MA income.

If you were a non-resident, it's easier to figure the MA portion first, then subtract it from the total deductions to get the non-MA portion.

To calculate the MA portion: Divide your MA-source income (subject to taxation by MA) by the total of all income that would be taxable by MA if you were a full-year resident. Multiply the resulting fraction by your total deductions.

If you were a part-year resident, divide the number of days you lived outside of MA by 365. Multiply the resulting fraction by your total deductions, to get the non-MA portion.