If you have an adult child without health insurance, now is your chance to get him or her covered.

As a result of the landmark health care bill passed this year, starting Sept. 23, employers have to allow children under age 26 to be added as a dependent on a parent's health insurance plan. Previously, firms often set an age limit of 19, or if a child was a full-time student, 23.

To get coverage, you must sign up during your employer's annual open-enrollment period, which generally occurs in October and November.

So to make sure your child does not miss out on an opportunity to get insured, here is what you need to know.

Who is eligible? Almost any child under the age of 26 qualifies to be added as a dependent to an employer-provided group health plan.

Unlike with some state laws, which extended coverage for adult children but often limited the benefit to kids who were still in school or who were financially dependent on their parents, there are very few restrictions once the rule kicks in.

An adult child can be married and still qualify. He or she does not need to be claimed as a dependent on a parent's tax return or be a student. And the child can live apart and in a different state.

In some cases, an adult child who has a job with employer-provided health benefits could still qualify as a dependent under a parent's policy. The one exception here: If the parent's health insurance plan is considered "grandfathered" (see box).

When do benefits begin? By law, employers have to provide a 30-day window to allow dependents up to age 26 to enroll.

Some employers may set aside a special enrollment period to sign up adult children. But the vast majority of companies will use their standard open-enrollment period during the fall to comply, said Debra Gold, a senior partner with the Mercer human resources firm. After you sign up, coverage generally starts when the company's new plan year begins, usually Jan. 1.

Need dependent coverage for the next few months? Consider a short-term policy. Check out eHealthInsurance.com.

How much will it cost? Employers cannot charge a special premium to add an adult child.

"This law provides for young adults to come on for the same cost as other dependents," said Sara Collins, vice president for affordable health insurance at The Commonwealth Fund, a private foundation that focuses on health care issues.

How much more could workers pay as a result of adding 20-somethings? Some estimates say premiums are expected to rise about an additional 0.7 percent in 2011, 1 percent in 2012 and 1 percent in 2013.

Today, the average annual premium for a family plan is $13,770, according to the Kaiser Family Foundation, which studies health care issues. Of that, workers pay 29 percent, or $3,997, annually. The employer picks up the rest of the tab.

E-mail Carolyn Bigda at yourmoney@tribune.com.

Grandfathered plans

The definition of a "grandfathered" plan is fairly nuanced, but generally it applies to policies that existed before the health care bill passed in March.

"An employer will have to tell you if it's grandfathered or not," said Debra Gold, of Mercer, a human resources firm.

Employers lose grandfathered status if significant changes are made to the plan, such as if the employer increases co-payments by more than 15 percentage points above medical inflation. Of those maintaining grandfathered status on at least one plan in 2011, about half expect to lose it before 2014, when even this restriction disappears.