2018 was the first year our family income resembled post-FIRE numbers on our tax returns. My wife worked half the year before FIRE'ing but we maxed out her 401k contribution and put some money in an IRA so our MAGI for ACA purposes still came in at 153% of the Federal Poverty Level. We also claim my dad as a dependent, since I support half of his expenses. We claim a $500 dependent credit for him, but because it is nonrefundable we aren't able to really take advantage of it because the tax on our income this year only amounts to $64, thanks to most of our income being qualified dividends after our $24,000 standard deduction.
I project our income ahead of time with a spreadsheet so I don't get any surprises come tax time. Our actual income this year was a little higher than I estimated, so our actual ACA Premium Tax Credit (PTC) was a little lower than what we received during the year, meaning I would need to repay $67 of that. The PTC repayment just gets lumped in with the rest of your tax, bringing our total tax owed to $131. However, because we are claiming the dependent tax credit for my dad we still owe $0 in tax, and we're leaving $369 of that credit on the table since it's nonrefundable.
In future years, if I were to estimate my PTC about $500 high, at the end of the year that overage that I would need to repay and the dependent tax credit we receive will cancel each other out, instead of leaving up to $500 of nonrefundable money on the table. I may or may not be able to do much with this for 2019 since I've already declared my estimated income during open enrollment, but it's an interesting observation that will be valuable in the future.
Of course, we'll still have to pay attention to the ACA brackets. If we're already maxing out a bracket and don't want to go any higher due to the loss of a Cost Sharing Reduction subsidy this may be of limited value, but it's worth noting.