Kenneth Weissenberg and his spouse, Brian Sheerin, pay an extra $5,000 a year in taxes because they are unable to file jointly as a married couple.

NEW YORK (CNNMoney) -- Same-sex spouses are paying as much as $6,000 a year in extra taxes because the federal government doesn't recognize gay marriage, according to an analysis conducted for CNNMoney by tax specialists.

While marriage provides tax benefits for many heterosexual couples, same-sex families don't enjoy the same perks because they are not allowed to file their federal returns jointly.









The imbalance persists despite increasing acceptance of gay marriage as a legal right. More than 12 states now grant full or partial marriage rights to same-sex couples, and a recent Gallup poll showed -- for the first time -- that a majority of Americans favor gay marriage.

But not the federal government, which is constrained by the 1996 Defense of Marriage Act. Even as more same-sex couples are able to file jointly at the state level, they are still forced to file as single when submitting federal returns to the IRS.

This means they can't combine their income and deductions to take advantage of lower tax rates. It's also harder for them to qualify for certain tax breaks because the credits phase out sooner for single filers.

"It's costing these families thousands of dollars a year, as well as the emotional pain and suffering," said Ken Weissenberg, a partner at accounting firm EisnerAmper who is in a same-sex marriage himself.

Why gay couples pay more: To zero in on the tax bill gap between same-sex families across the country, CNNMoney asked H&R Block to crunch number comparing same-sex and heterosexual families according to a variety of scenarios. (Check out H&R Block's methodology)

One scenario involved families with one spouse earning $100,000 and the other spouse staying at home with the family's two kids.

In the same-sex family's case, the working spouse files as "head of household," and the stay-at-home spouse is considered a "qualifying relative."

Say that couple reported no other income or deductions. In that case, the same-sex household's federal tax bill is $15,199, which includes tax the head of household must pay on health insurance premiums to cover the stay-at-home spouse. That's $4,543 higher than the straight couple's liability.

Why? Because the "head of household" designation comes with some disadvantages.

Filing as "head of household" instead of "married filing jointly" exposes more income to a higher tax bracket. Plus, standard deductions, which are given based on the filing status to taxpayers who don't itemize deductions, are lower for a head of household than they are for married couples filing jointly.

And then there are the kids. When a child tax credit is claimed, the gap between same-sex households and married couples can grow even wider.

The heterosexual couple in H&R Block's example is able to claim the full $1,000 child tax credit for each kid. But the credit phases out sooner for families claiming "head of household." So in this case, the cost of being unable to file jointly comes out to $6,043 for same-sex households.

The one exception where same-sex spouses can actually come out ahead is the so-called marriage penalty. For some same-sex spouses in the higher tax brackets who work and have no children, filing tax returns using the "single" status makes the liability a little lower than that of heterosexual married couples. Still, "single" status is typically less advantageous than "married filing jointly."

Other factors driving up the bill: It's not just income taxes that are costing same-sex couples more.

Many same-sex spouses don't qualify for the same marital exemptions given to other families for inheritance taxes and gift taxes. In addition, same-sex households receive lower tax exclusions for capital gains on the sales of a home (unless the home is jointly owned and each spouse qualifies for the exclusion).

All of this is not only costing same-sex couples more, but it's a paperwork and compliance nightmare.

Same-sex families who live in states where gay marriage is recognized typically have to fill out up to four separate returns -- including mock federal returns -- to cover both their state and federal taxes. Plus, hiring a tax preparer to take on these more complicated returns tends to be significantly more expensive.

"But it shouldn't stop anyone from getting married," said Weissenberg, who says he pays an extra $5,000 in taxes per year simply because he is in a same-sex marriage. "If I had to pay twice as much in taxes to be married to my husband, I would."