You have it exactly right. The amount of the conversion is included in your income -- as ordinary income -- in the year you do the conversion. That will definitely impact your subsidy for ACA insurance, and may impact other benefits as well, if they are based on income.PLUS, you'll want to pay the taxes on this conversion with money held outside the 403(b) plan. So it will soak up some of your other liquid assets. This may not be a wise move considering all the implications.