People over 50 say their top retirement financial worry is health-care costs, a survey, out Friday, shows.

But only 15% of pre-retirees have tried to figure out how much money they might need for health care and long-term care in retirement, according to the survey of 3,300 people, ages 25 and older, conducted by Merrill Lynch in partnership with Age Wave, a research think-tank on aging issues.

It's no wonder people are worried. Another report estimated that out-of-pocket health-care costs in retirement may equal $318,800 if retirement lasts 30 years; $220,600 for 25 years; $146,400 for 20 years; $91,200 for 15 years; $50,900, 10 years. These estimates do not include the cost of long-term care.

"People are quite enthusiastic about the chance of living a longer life, yet at the same time there is mounting worry about the cost of health care in retirement, and very few people have sat down and figured out what that will be," says gerontologist Ken Dychtwald, CEO of Age Wave.

More from USA Today: Do retirees need long-term care insurance? Employer health plan deductibles see big 5-year jump Health care spending growth is slow but rising

Financial planning for retirement needs to include health-care costs, says David Tyrie, head of retirement for Bank of America Merrill Lynch. People should realize that "investing in your health could have the biggest impact on your wealth."

When it comes to their greatest health worries in retirement, 63% of those 50 and older say not being able to afford health care and long-term care expenses; 39%, side effects of multiple medications; 37%, not being able to manage chronic pain; 34%, not finding doctors who can effectively meet their needs as they grow older.

Health tops wealth when it comes to a happy retirement, the survey found. Most retirees say having good health is the most important ingredient for a happy retirement, followed by financial security, having loving family/friends and having purpose.

Read MoreStudent Loan Debt Burdens More Than Just Young People

The survey also showed that more than half (55%) of retirees retired earlier than they had expected; 38% retired when they expected; 7% later than they expected. The main reasons people gave for early retirement: personal health problems, followed by job loss.

Follow this link:

Health-care cost top retirement concern