Your AGI has an impact, of course, but how much you had withheld has nothing to do with it. It has to do with your tax liability after you take your AGI and reduce it by standard or itemized deductions (and qualified business income deduction, if applicable) to arrive at your tax liability and then reduce that by other tax credits you may have that must be first applied before a net liability - the extent to which you may use your hybrid credit. If you have a net liability of $10,000 before your hybrid credit, you will owe $2,500 and you will be refunded $6,200 ($8,700 less $2,500). If you have a net liability of $6,000 before your hybrid credit, you will be refunded only your withholding of $8,700, as you may use only $6,000 of your hybrid credit to bring the taxes you owe to $0. They hybrid credit, unlike the "refundable" child care tax credit, is "nonrefundable." It may be used only to the extent of taxes you owe and can be used to that extent only in the year it is generated. There is no carry-back or carry-forward.
