Yes. You’ll owe a 5 percent late-payment penalty on any tax not paid by due date of the return, even if you’ve filed an extension.
If you file your return more than 30 days after the due date, including an extension, a 20 percent late-filing penalty will be added, and you’ll owe a total penalty of 25 percent of any tax not paid.
Employers who knowingly fail to deduct and withhold the tax may be subject to a penalty of $250 per employee, up to $25,000 for each tax period, in addition to any other penalties or interest.
Interest is charged on any unpaid tax if you don’t pay the tax by the due date. The interest period begins the day after the tax is due on all unpaid tax from the due date until the tax is paid.