The federal individual mandate penalty is zero, but several states require residents to carry coverage or pay a state penalty. California, Massachusetts, New Jersey, Rhode Island, and the District of Columbia have their own mandates.
Five jurisdictions enforce a penalty: California, Massachusetts, New Jersey, Rhode Island, and Washington, D.C. Vermont has a mandate with a reporting requirement but no penalty. Everywhere else, only the (currently $0) federal rule applies.
There’s no federal penalty; the ACA individual-mandate penalty has been $0 since 2019. But a handful of states impose their own penalty if you go without coverage.