The IRS will send a notice of the interest due. I received an IRS notice resulting from correspondence I sent regarding a change to my return. The notice includes additional penalty and interest charges. Interest is charged on any unpaid tax from the due date of the return until the date of payment. The interest rate is determined every three months and is the federal short-term rate plus 3 percent.
Interest is compounded daily.
In addition, if you filed on time but didn't pay on time, you will generally have to pay a late payment penalty of one-half of one percent of the tax owed for each month, or part of a month, that the tax remains unpaid after the due date, up to 25 percent. The one-half of one percent rate increases to one percent if the tax remains unpaid after several bills have been sent to you and IRS issues a notice of intent to levy. When calculating your tax liability to determine whether you need to make an estimated tax payment, your total tax for the year should include the amount of the 10 percent additional tax on early distributions from qualified retirement plans unless any exception applies. Tax on early distributions from retirement plans Estimated quarterly income taxes for a corporation were not paid. If the corporation does not pay a required installment of estimated tax by its due date, it may be subject to a penalty.