GST applicability on penal interest clarified: penal interest on notified supplies excluded from GST, principal supply value unchanged. Where additional or penal interest is charged in relation to a transaction whose underlying supply is covered by Sl. No. 27 of Notification No. 12/2017 Central Tax (Rate), that penal interest is not subject to GST because it is not covered by the notification; the value of the principal supply for levy of GST remains as stated in the illustrative scenario.