If you do not claim your son as a tax dependent, he cannot be covered as a dependent under you and your spouse’s Marketplace plan and apply his tax credit to your premium. The federally-facilitated Marketplace (HealthCare.gov) does not currently allow multiple tax households to enroll in a plan together and apply any combined tax credits to the premium. Since your son is not claimed as a tax dependent, he would be considered a separate “tax household” of one, while you and your spouse will be counted as a household of two (assuming you do not have any other children). If you live in a HealthCare.gov state, your son must apply separately for coverage and his eligibility for premium tax credits will be based on his income alone. Note that this means your son will have his own separate deductible and maximum out-of-pocket cap under his policy. He can then apply the tax credits the Marketplace calculated for him to reduce the cost of his premium. If your state does not use HealthCare.gov, contact your state Marketplace for instructions on applying for coverage and financial assistance as a family comprised of multiple tax households.