Time of supply rules when tax rates change determine whether invoice date or payment date governs the taxable moment.

Change in rate of tax fixes the time of supply: for supplies before the change, the earlier of invoice date or payment governs when both occur after the change; invoice governs if issued before the change and payment after; payment governs if received before and invoice after. For supplies after the change, payment governs if received after but invoice before; the earlier of invoice or payment governs if both before; invoice governs if issued after but payment before. "Date of receipt of payment" means earlier of book entry or bank credit, subject to a bank-credit timing exception.

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