Section 426 - Interest on excess refund.

Taxpayer must repay provisional refund with 0.5% monthly simple interest on amounts not due until regular assessment

Where a refund previously granted to a taxpayer under a provisional procedure is either not due on the eventual regular assessment or exceeds the amount refundable on regular assessment, the taxpayer must pay simple interest at 0.5% per month (or part month) on the whole or excess refunded from the refund date until the date of the regular assessment. If a later order upholds the refund in whole or in part, the interest payable under this rule is reduced accordingly. An assessment made for the first time under the specified provision is treated as a regular assessment for these purposes.