If you did not make a payment of your estimated tax due at the time that you requested an extension---by April 15-- then, yes you will be subject to paying interest on the amount owed. You were supposed to pay your estimated tax due by April 15 even if you have had an extension to file.
**Disclaimer: Every effort has been made to offer the most correct information possible. The poster disclaims any legal responsibility for the accuracy of the information that is contained in this post.**
