Time of supply on tax rate change depends on invoice or payment timing and the bank credit rule. Determination of time of supply when tax rates change depends on whether the supply occurred before or after the rate change and on the sequencing of invoice issuance and payment receipt. If both invoice and payment occur after the change, time of supply is the earlier of payment receipt or invoice date; if invoice precedes and payment follows the change, invoice date governs; if payment precedes and invoice follows, payment date governs. Where bank credit occurs more than four working days after the change, the date of bank credit is treated as the date of receipt.