I imagine they'd keep track of your withholding, so the "bill" would be for the difference between what you'd paid already and what you owe. Just like your cur

I imagine they'd keep track of your withholding, so the "bill" would be for the difference between what you'd paid already and what you owe. Just like your current tax return. In the case of a refund, it might even take the form of a check that, if cashed signifies your intention not to file a return.