They probably made a little more money than they estimated when they signed up. There"s a supplement that depends on income. The supplement is given to people with incomes as high as the $300k+ range. Trump had a change made to limit the clawback to just the amount it would be for the actual income you made. Prior to that, they wanted the entire supplement back if your income was higher than estimated. The last year it was done that way, I made $4,300 more than I estimated. I got a $34,000 extra tax because of that. I found out that I could contribute $4,300 to my IRA for the year before(which is the year of tax I was paying) which is allowed up to April 15th. As a result, I got an $800 refund on my Fed taxes that year. Crazy!