For millions of Americans without health insurance, the clock is ticking.

Today is the last day of open enrollment on, the federal health insurance marketplace created by the Affordable Care Act, commonly known as Obamacare. Anyone who enrolls by January 15 and pays their first monthly premium on time will be covered starting on February 1, 2022.

During open enrollment, anyone can sign up for coverage for any reason. But after the period closes, only those with a change in circumstance—such as the loss of a job or a big life change like marriage or divorce—can sign up.

A record 13.6 million people had already signed up for health insurance coverage through the federal and state-based marketplaces for coverage starting January 1. Of those, nearly 12 million people were returning enrollees and 2 million were new to the marketplaces altogether.

According to the Commonwealth Fund’s most recent Biennial Health Insurance Survey, in the first half of 2020, 12.5% ​​of non-elderly US adults were uninsured. Another 43% were underinsured, defined as having out-of-pocket health insurance costs representing at least 10% of household income (less for lower-income people) or having a deductible at least 5% of household income.

People sometimes only discover that they’re underinsured when they need healthcare services and realize they don’t actually have much coverage.

This happened to a self-employed woman who recently reached out to Nicole Broadhurst, a board-certified patient advocate and lead medical billing advocate at Tennessee Health Advocates.

Newly diagnosed with breast cancer, the woman’s health insurance was limited to covering a maximum of $10,000, according to Broadhurst.

“Suddenly, her health insurance benefits became a priority,” Broadhurst said. “We worked hard to find her an ACA-compliant policy to enroll in before the deadline today. Without the Affordable Care Act policies, she would have been unable to locate coverage due to the preexisting cancer diagnosis.”

Health insurance sold on the marketplace must include certain consumer protections, such as prohibitions against denying coverage for people with preexisting conditions, and coverage requirements, including mandatory coverage for 10 essential health benefits.