Boost your federal income tax withholding if you expect to owe a lot to IRS. It can help avoid an underpayment penalty. You’re off the hook from the fine if you prepay at least 90% of your 2018 tax bill or 100% of what you owed for 2017 (110% if your 2017 adjusted gross income was more than $150,000). The new tax law and revised IRS tax withholding tables provide even more incentive for you to check that income taxes withheld from paychecks, retirement distributions, pensions, etc., are accurate for your circumstances. If you need to prepay additional taxes for 2018, you can have more tax withheld from Dec. paychecks or a year-end IRA distribution. Tax withheld at any point during the year is treated as if paid evenly during the year.