IRS gives some welcome relief on the underpayment penalty for 2018. Generally, you escape the fine if you prepay, either through withholding or by making estimated tax payments, the lesser of at least 90% of your 2018 tax bill or 100% of what you owed for 2017 (110% if your 2017 AGI was more than $150,000). The Service knows that many individuals likely didn’t adjust their withholding or estimated tax payments to account for all the changes in the new tax law. Preparer groups and others have been urging IRS to fully waive the penalty for 2018. The agency isn’t going that far, but it has decided to lower the 90% threshold to 85%. You have to request the waiver on Form 2210 and attach page 1 of the form to your federal return. The instructions for the 2210 have the complete details.