The average 65-year-old couple retiring in 2010 would need $250,000 to cover health care costs over the course of their retirement years, according to Fidelity Investments.

Benefits consultants at Fidelity, Boston, are basing those projections on results from a survey of 376 married individuals ages 65 years or older who are not working full-time.

Fidelity consultants found that 47% of surveyed seniors reported paying more each month for insurance premiums and out-of-pocket health care costs than they had expected in retirement. Only about 33% of the retirees reported saving expressly for health needs in retirement during their working years.

Health care costs are averaging $535 per month for retirees interviewed, or about 20% of an average couple’s $2,842 in total monthly expenses. Among those surveyed, 11% said their health care costs are $1,000 per month or higher.

When asked to identify their single biggest financial concern today, around 33% of the survey participants said paying for health care and long term care expenses such as a nursing home are among their biggest worries.

Other financial concerns include paying for daily living expenses such as food, transportation and utilities (17%), assisting grown children and grandchildren with their financial needs (10%) and paying for housing (7%). Of retirees surveyed, 35% said they have no financial worries.

Earlier this year, the Center for Retirement Research at Boston College predicted that a typical married couple free from chronic disease could expect to spend $197,000 on health care costs, excluding long term care costs.