Beginning this month, you can sign up for a new 2016 health insurance policy on the health insurance Marketplace. You can also change or renew the policy you purchased during the last enrollment period. Even if your current policy has an automatic renewal feature, you'll want to verify that you are still eligible for the federal premium tax credit.
What if you didn't sign up last winter and didn't have health insurance coverage in 2015? You may owe a penalty on your 2015 federal income tax return. The penalty for 2015 is the greater of $325 per adult and $162.50 per child under 18 (up to a maximum per-family penalty of $975) or 2% of your modified adjusted gross income (with a maximum of the national average premium for a Bronze plan).