Tax payments were due April 18, even if you had an extension to file the return. If you owed tax and didn't make an estimated payment, the penalty plus interest for late payment is about 1% per month.
If you don't file the return "on time", the penalty is 5% per month (or partial month) of what you owed in taxes. If you filed October 23, that counts as one month late.
But if you didn't owe taxes and are expecting a refund, there is no penalty even if you are late because the penalty is a percentage of what you owe.
