Federal tax underpayment scenarios can arise for salaried (W-2) workers as well. This situation occurred when you didn't withhold enough taxes from your paychecks, if you claim the wrong number of allowances on your W-4, you could wind up in an underpayment scenario. Similarly, if you're a salaried worker who earned a lot of outside income during the year (say, through investments), you could easily wind up underpaying your taxes even if you filled out your W-4 correctly.
