In 2016, the FPL is projected to be $11,800 for a single person and about $24,000 for a family of four.
The largest number of those paying a fine are expected to be those earning more than 500% of the FPL, or nearly one million people, but one third of those paying a penalty will be those earning 400% or more of the FPL, paying an amount that will be about two-thirds of the $4.2 billion.
It remains unclear, however, how the IRS will collect much of those funds and whether audits specifically geared to examining tax returns for health plan premium payments will be ordered.
Earlier this year, some Republicans estimated that the IRS would have to hire as many as 16,500 new agents, much of the added $10 billion a previous CBO estimate said the IRS would need to enforce the Patient Protection and Affordable Care Act.
It's also unclear whether the people who avoid paying either health plan premiums or the penalty are more likely to be those healthy, young citizens who don't think they will need healthcare or that they could possibly be caught.