In itself, it certainly is NOT "tax due" on Line 12a of Form 1040.
Were you (or your spouse) self employed, and did you claim the Self Employed Health Insurance deduction? If not, it is NOT added to your taxable income either. However, if you received a 1099-MISC, you can avoid an IRS letter by entering it as income, then 'backing it out' by another entry using the negative amount.
If you received the Premium Tax Credit, that SOMETIMES could be a "gray area". In MOST cases, the Premium Tax Credit is NOT based on the amount of the Insurance Premium (it is based on the Second-Lowest-Cost-Silver-Plan, or SLCSP). If that was the case with you and would continue to be true using the lower modified insurance premiums (after the MLR you received), then NOTHING would be changed, and you would not need to worry about anything because it will NOT affect your tax return.
In a few cases the amount of the Premium Tax Credit is based on the amount of the insurance premium. It that was the case with you (or if it would be the case if you used the modified amounts, after the MLR), then that is the "gray area". It is a "gray area" because logic and math would dictate it SHOULD affect your tax return (some or all could be added to the "tax due"). However, as far as I know, the IRS has NOT addressed this point.
