In some cases, transferring funds from one H.S.A. to another can take weeks, during which the original account continues to charge a monthly fee, the report said. It also cited consumer complaints about funds that were lost during the transfer from one bank to another.

The research firm Morningstar evaluated 10 H.S.A. plans in October using criteria like fees, interest on savings and investment choices. (The firm looked only at accounts available directly to individuals, rather than those offered through employers, so details may vary.) Fidelity Investments was the only provider rated “high” overall for both spending and investing. Its H.S.A. offered an interest rate on savings well above 2 percent, while its competitors paid less than 1 percent.

“That’s a big shortcoming,” said Greg Carlson, senior manager research analyst at Morningstar.

Here are some questions and answers about health accounts:

How can I best avoid having money left over in an F.S.A.?

Sara Taylor, senior director of employee spending accounts at the benefits consultant WTW, suggests taking a close look at your past medical expenses before deciding how much to contribute to your F.S.A. “It’s hard to do, for some people,” she said. But looking at your “explanation of benefits” for last year — the forms that describe what treatments you had and what share of the cost you owe — can help you come up with a reasonable number. Was last year an anomaly because you had major surgery? If so, you may want to contribute a lower amount. Many employers offer online tools to help you make an estimate.

It also helps to know what you can spend F.S.A. money on. That way, if you find yourself with a balance at the end of the year, you can use the money to buy eligible over-the-counter items like pain medication and even sunscreen. A helpful resource is the F.S.A. Store, which includes an online alphabetical list of eligible and ineligible items.

If I forfeit cash in my F.S.A. to my employer, have I wasted my money?

No one wants to give up funds, but workers can still come out ahead, compared with not contributing, because of the tax benefits of F.S.A. contributions, Mr. Spiegel said. Say a hypothetical worker with a 30 percent marginal tax rate (including federal, state, payroll and local taxes) contributes $1,500 to an F.S.A., realizing $450 in tax savings. If the worker forfeits less than $450 back to the employer, the worker will still have benefited from participating.