In the past, if lawmakers did nothing in the open enrollment period, their coverage would automatically continue. This year, by contrast, they must affirmatively pick a plan. Their coverage under the federal employee program will end on Dec. 31. If they do not choose a plan via D.C. Health Link by Dec. 9, they will lose the government contribution to their premiums and could lose their right to retiree health benefits as well.

In addition, lawmakers who go without insurance next year may, like other Americans, be subject to tax penalties.

Some congressional aides, especially older employees who face higher premiums, are unhappy about the changes. But some who carefully compare their options on the exchange find that they can save money.

Jacqueline A. Thomas, a 26-year-old legislative correspondent for Representative Debbie Wasserman Schultz, Democrat of Florida, said she was able to reduce her monthly premium to $60, from $120, by switching to a Kaiser plan from a Blue Cross and Blue Shield plan.

“I’ll be paying half as much for comparable coverage,” she said.

The congressional work force is full of young, healthy people like Ms. Thomas, precisely the type of customer insurers want to attract.

Congressional aides naturally have a few complaints. Some are confused by the large number of options. When they sign up for a plan online, they get no confirmation, so they are apprehensive. In addition, the website for the local exchange does not display the government contribution for members of Congress and their aides.

It shows, for example, that a couple with one child may pay $1,300 a month for a plan, when, in fact, their share of the premium is only $352; the government pays $948. Local exchange officials said their website had not been set up to calculate premium contributions using the formula required for lawmakers and other federal employees.