I believe that the IRS will only debit the authorized amount, but then they will send you a bill for penalties and interest.
The penalty for late filing is 5% of the amount owed for up to 5 months, then 0.5% after that. Since you are just under 5 months late, there will be a 25% penalty for late filing.
The penalty for late payment is 0.5% per month, but is not charged for any month when you are being charged the 5% late filing penalty.
Then you owe interest (around 4% annual percentage rate) on the total amount owed. So the total penalties and interest should add up to around $435 more or less.
