My employers neglected to take out any federal income taxes from my paychecks for all of 2021. Social security and state taxes were still being deducted and I only work 2 days a week. My checks were already so low it never occurred to me that I was being overpayed. I definitely didn't fill out my w4 and ask to have zero deductions, and they deducted everything just fine the previous year. I feel like a moron for not looking more closely at my stubs.