What is the irs penalty for late payment of estimated taxes?

The late payment penalty is 0.5% of the tax due after the due date, for each month or part of the month that the tax remains unpaid, up to a maximum of 25%. You won't have to pay the penalty if you can show that there is reasonable cause for not paying on time. Once the due date has passed, the IRS will normally return 0.5% of the total amount you owe.