Time of supply determines when service tax arises; invoice, payment, provision or recipient books can trigger liability. Time of supply of services is the earliest of invoice issuance (if timely), receipt of payment, provision of service (if invoice late), or entry in the recipient's books. For reverse charge, it is the earlier of recipient payment or the date immediately following sixty days after supplier invoice, with recipient book entry as fallback. Voucher supplies use voucher issuance or redemption. If primary rules cannot determine time, the date of the periodical return or tax payment applies. Additions to value for interest, late fee or penalty are timed when received by the supplier.