Additions.

(a) Failure to file tax return. In the event of failure to file any return required under § 117.1 (relating to general requirement of a return) on the date prescribed therefor (determined with regard to any extension of time for filing), there shall be added to the tax required to be shown on the return the amount specified in subsection (b) unless the failure to file the return within the prescribed time is shown to the satisfaction of the Department to be due to reasonable cause and not to wilful neglect. The amount to be added to the tax is 5% thereof, if the failure is for not more than one month, with an additional 5% for each additional month or fraction thereof during which the failure continues, but which shall not exceed 25% in the aggregate.

(b) Penalty imposed on net amount due. The amount of tax required to be shown on the return for the purposes of this section shall be reduced by the amount of any part of the tax which is paid on or before the date prescribed for payment of the tax and by the amount of any credit against the tax which may be claimed on the return.