If you do not file by the deadline, you might face a failure-to-file penalty.
If you do not pay by the due date, you could face a failure-to-pay penalty.
The failure-to-file penalty is generally more than the failure-to-pay penalty. So if you cannot pay all the taxes you owe, you should still file your tax return and explore other payment options in the meantime.
The penalty for filing late is usually 5 percent of the unpaid taxes for each month or part of a month that a return is late. This penalty will not exceed 25 percent of your unpaid taxes.
If you file your return more than 60 days after the due date or extended due date, the minimum penalty is the smaller of $135 or 100 percent of the unpaid tax.
You will have to pay a failure-to-pay penalty of ½ of 1 percent of your unpaid taxes for each month or part of a month after the due date that the taxes are not paid. This penalty can be as much as 25 percent of your unpaid taxes.
If you filed an extension and you paid at least 90 percent of your actual tax liability by the due date, you will not be faced with a failure-to-pay penalty if the remaining balance is paid by the extended due date.
If both the failure-to-file penalty and the failure-to-pay penalty apply in any month, the 5 percent failure-to-file penalty is reduced by the failure-to-pay penalty. However, if you file your return more than 60 days after the due date or extended due date, the minimum penalty is the smaller of $135 or 100% of the unpaid tax.
You will not have to pay a failure-to-file or failure-to-pay penalty if you can show that you failed to file or pay on time because of reasonable cause and not because of willful neglect.

Fact about penalties and interest is a post from: Fresh Start Tax Blog

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