There is no minimum penalty, which means that no penalty is assessed on zero-balance or refund returns. If you file your return on time but do not pay the tax you owe until after the due date, you will be subject to a late payment penalty. The rate for the late payment penalty is the same as the rate for the late filing penalty. The late payment penalty is not applied to any month for which the late filing penalty has already been assessed or paid. The late payment penalty is not applied when additional tax is assessed on a return filed in good faith, as is the case with most audit adjustments.
Interest is accrued on the additional tax, however.
In addition, a late filing penalty had already been imposed for one month of the delinquent period. Therefore, an application for extension is made in the form of a tentative tax return. If you file your return after the extended due date, the extension is void and you will be subject to the late filing penalty. If you file within the extended period, but do not pay the tax due until after the extension expires, the extension penalty will be assessed for the period of the extension, and a late payment penalty will be applied for the remainder of the period during which the tax remains unpaid. The computation of the extension penalty and late payment penalty is shown below.