Same sex couples who are legally married in a jurisdiction that recognizes same sex marriage will be treated as heterosexual married couples under the Federal Tax Code, for gift, income and estate tax purposes, no matter where they eventually live under a ruling made by the Department of the Treasury and the IRS. As a result, lawfully married same-sex couples no longer have to declare themselves unmarried on federal income-tax returns. Same-sex spouses won’t have to pay tax on health-insurance benefits they received through a spouse, an item that cost the average same-sex couple over $1,000 a year in extra tax, according to the Human Rights Campaign. The change could be especially significant for estate taxes, where spouses enjoy big advantages. Any same-sex marriage legally entered into in one of the 50 states, the District of Columbia, a U.S. territory, or a foreign country will be covered by the ruling. However, the ruling doesn’t apply to registered domestic partnerships, civil unions or similar formal relationships recognized under state law.