Underpayment Penalty

What is an underpayment penalty?

An underpayment penalty is an IRS charge for not paying enough tax throughout the year through withholding or estimated payments. The penalty applies when you owe more than $1,000 at filing time and have not paid at least 90% of current year taxes or 100% of prior year taxes. High-income taxpayers must pay 110% of prior year taxes to avoid the penalty.

How the penalty is calculated

The penalty is essentially interest on the underpaid amount for the period it was underpaid. The IRS sets rates quarterly based on federal short-term rates. The penalty applies separately to each quarterly payment period, so paying a large fourth quarter estimated payment does not eliminate penalties for earlier quarters. Form 2210 calculates the penalty if you use the annualized income method.

Avoiding underpayment penalties

Review your withholding and estimated payments quarterly. If income increases significantly, adjust withholding or make larger estimated payments. Safe harbor rules protect you: pay at least 100% of last year's tax liability through withholding and estimates. For AGI over $150,000, the safe harbor is 110% of prior year. Your accountant can run projections mid-year to avoid surprises.