Do I have to pay the full COBRA premium?

That's right. You can buy COBRA for up to 18 months -- the entire eligibility period -- but you must pay the full tab for the last three months.

COBRA -- Consolidated Omnibus Budget Reconciliation Act of 1986 -- was created as an amendment to the Employee Retirement Security Act to provide a safety net for people who lose their group health insurance coverage after they resign or lose their jobs. It also protects spouses and children who are covered by the plans.

The law gives you the right to continue your coverage under the group health insurance plan for up to 18 months at your own expense. And in many cases your spouse and children are eligible for coverage even longer, sometimes for up to three years.

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Although the coverage is useful, it's also expensive. A report by nonprofit group Families USA showed COBRA premiums eat up 84 percent of the average monthly unemployment benefit. To help offset those costs, the American Recovery and Reinvestment Act of 2009 provided a COBRA premium subsidy for people who lost their jobs between Sept 1, 2008 and May 31, 2010.

You can continue to get that premium subsidy, as long as you met eligibility requirements in that time frame. But you must pay the full amount to continue your COBRA coverage beyond the 15 months. For more, read know your COBRA rights.