Linnell and Chalmers say they are reminded at every turn that their inability to marry takes a financial toll, even on 11-year-old Paige. For example, there's the extra $3,600 Linnell pays each year because he cannot piggyback, as a spouse could, on the health insurance policy Chalmers gets as a teacher.

"We have a college fund set aside for Paige," said Chalmers, who earns about $60,000 a year, about the same as Linnell's pay as a nurse. "I'd like to see that $3,600 going towards that fund. Part of the reason we participated in the lawsuit was securing her future."

The Northbridge couple, together for 15 years, are among the plaintiffs in a closely watched lawsuit that says same-sex couples have the right to wed under the state constitution. Massachusetts' highest court, the Supreme Judicial Court, is expected to rule on the case this year — and, plaintiffs hope, make the state the first to permit gay marriage.

For many gay couples, the inability to marry adds up to real expenses, say lawyers and financial planners who specialize in advising nontraditional couples.

Some costs hit couples of any age. For instance, while some companies offer employee health benefits to their employees' domestic partners, the partner must pay federal income taxes on the value of the benefit, which a spouse could receive tax-free.

Other costs manifest themselves later in life — especially upon the death of one partner — when pension benefits may be compromised, property transfers complicated, or 401(k) savings subject to taxes years before they might be for a surviving spouse. And Social Security benefits, which in some cases can be tapped by a surviving spouse, are essentially untouchable by a surviving domestic partner.

"We've taken all those legal precautions we think we can take," said Chalmers. "It seems like every day or every month, we find out there's another piece we haven't covered, where if we had the right to be civilly married in Massachusetts, all these things would be automatic."

But Chalmers and Linnell also acknowledge a point made by financial planners — financially, some gay couples are better off unmarried, finding ways to save themselves money. Planners emphasize that neither they nor the IRS necessarily condone such maneuvering, but they say some of these practices are common:

• When one unmarried partner earns considerably more than another, deductions and charitable contributions may be shifted to the higher earner's tax return.

• When gay parents have two children, they may be able to double — to $10,000 — a deduction for childcare expenses simply by making each child the dependent of a different parent.

• Later in life, if the poorer of two parents claims the child as a dependent, the richer parent may be invisible to college financial aid offices, which may result in a better deal.

Ronald Crews, president of the Massachusetts Family Institute, which opposes gay marriage, said he regrets that some gay couples pay more because they can't marry. But he said that's no excuse for changing the definition of the institution of marriage.

"In life we don't get everything we want, and that's because some things just mean what they mean and we have to accept the consequences for that," Crews said.