First, review your most recent paystub to confirm whether any federal income tax was withheld. There is no requirement from the IRS that W-4s must be provided each year. They are only needed when a employee begins working or if there are changes in the employee's withholding status (i.e. single to married). If you have an old W-4 on file with your employer, they should be using that information to calculate your income tax withholding. And if you never filled one out, they should have used the default withholding amount which is single, non-exempt. However, if after reviewing your most recent pay stub and you find that no federal income tax has been withheld for the entire year, you'll likely need to make an estimated payment by January 15, 2021 if you expect to owe more than $1,000. To avoid an underpayment penalty, you'll need to pay the smaller of 100% of the tax shown on your 2019 return or 90% of the tax you expect to owe for 2020. But start with talking with your payroll department today to get this corrected for 2021.