How to calculate interest due on filing after 4/15.

[tyu1127]

I did request an extension for both Fed and State (AZ), but I paid no estimated tax at that time, now it appears that I do owe taxes and would like to ensure that I pay the correct amount. (Tax due plus interest)

[Texas Roger]

The amount of interest owed depends on when the IRS and state taxing authority actually receive your tax return and payment. It is not possible to calculate it accurately. Just pay the amount of tax due and the IRS and state taxing authority will send you bills for the interest owed.