Underpaying or missing an estimated tax payment may result in underpayment penalties and interest charges. The IRS requires taxpayers to pay their estimated tax liability throughout the year to avoid penalties. If you underpay or miss a payment, you may be subject to the underpayment penalty, which is calculated based on the amount of underpaid tax and the number of days the payment is late. It is important to review the IRS guidelines or consult with a tax professional to understand the penalty calculation and ensure timely and accurate estimated tax payments.