10% Penalty for Failure to Timely File a Return: If you do not file your return by the due date and at least 90% of the correct tax is not paid, you owe an additional 10% of the unpaid tax.
5% Penalty for Failure to Timely Pay the Tax Due:If you file your return on time but do not pay at least 90% of the correct tax due, you owe an additional 5% of the unpaid tax.
You will never be subject to both penalties. The penalty will be the applicable 5% or 10%, but not 15%.
The interest rate may change yearly. Interest must be added to delinquent tax at 0.5% per month rate, beginning on the due date of the return and accruing each month until you make full payment of all tax, penalty, and interest due.