Whether or not you are penalized for filing late depends on if the Tax Return you file has a Refund or a Balance Due.
If you are owed a refund for the tax year, you have three years from the original due date of the return to claim it. Once you file the return, you will also be paid interest on the refund...so definitely no penalty in this case!
On the other hand, if you have a Balance Due on the Past Due Tax Return, the IRS will add a penalty for filing late and interest on the balance due.