Tax balances are due on April 15th (unless extended).  Filing for an automatic extension (to October 15th) does not change the date the tax is due; it only changes the date the return is due.  Interest and penalties will still accrue beginning on April 15th.  Extensions are designed for taxpayers who have not been able to get all their required documents together before the filing date.  If you have all the information needed to file your return, you should do so, even if you don’t pay the balance due.  Interest charged on past due balance is 0.5% per month; the penalty for not filing is 5% per month.