(MONEY Magazine) – An estimated 370,000 men and women over 65 live together. one reason so many stay single is that marriage can erode the financial security that seniors like Hilde Waring, 74, and Marvin Goldman, 72, depend on in retirement. The Bronx couple (below), both widowed, file separate returns and keep more after tax than if they combined their incomes. "Some years ago I might have gotten married," Waring says, "but certain things have changed my mind, mainly Social Security and taxes." Details:

-- SOCIAL SECURITY. Two singles living together can each have an income of $25,000 before their benefits are subject to tax. A married couple filing jointly is limited to $32,000. Social Security pays Goldman about $6,000 a year, whereas Waring receives a larger amount, plus income from a trust set up by her late husband. Marriage would result in more of their benefits being taxed.

-- PENSIONS. Remarriage can mean you forfeit your deceased spouse's benefits. Unmarried partners receive no survivor benefits, but the retiree can take a lump-sum distribution and buy an annuity with a survivor benefit for the partner.

-- HOME OWNERSHIP. Homeowners over 55 have a one-time capital-gains exclusion up to $125,000 on the profit from a house sale. But marry someone who has already taken it, and you'll forgo yours unless you divorce or become widowed.

-- MEDICAID. Though eligibility rules vary by state, a married couple may have to deplete a significant portion of their jointly owned assets before Medicaid will pay for long-term nursing-home care for the sick spouse. The assets of the healthy partner of an unmarried couple are not counted in the eligibility criteria. The only exception is property you transfer to your partner in the three-year period prior to applying for Medicaid and after entering a nursing home.

For more information about the finances of unmarried couples of any age and sex, check out The Living Together Kit (Nolo, $24.95).

--Roberta Kirwan