Time of supply for penal interest: tax point is receipt date and such interest may be included in supply value. Time of supply for additions to value by interest, late fee or penalty is the date the supplier receives such addition; tax on that amount is payable for the tax period containing that receipt. Invoice-timing rules under Section 31 and Rule 47 determine timings for service supplies, with special provisions for continuous supplies, milestone payments and certain financial entities. Penal interest may be included in the value of the principal taxable supply and taxed at the rate applicable to that supply, unless charged by a separate financier and covered by an exemption notification.