According to the new numbers from the Department of Treasury, 2 to 4 percent of taxpayers will owe a penalty for not having health insurance last year. That’s approximately 3 million to 6 million households. But who has to pay — and what happens if they don’t?

The penalty this tax season is $95 per adult — about half that per child — or 1 percent of household income, whichever amount is  higher. The fines will also keep going up. Not having insurance in 2015 will cost $325 per adult or 2.5 percent of household income. In 2016? 2.5 percent or $695 per person and tied to inflation in the years that follow. 

It’s unclear how many will actually have to pay up, however. Many groups are exempt from the penalty and the IRS’ ability to enforce could be limited, especially after recent budget cuts.

For more, listen to the story in the audio player above.