COM80230 | how interest is calculated: common period rules - reallocating from tax to penalty or interest (Action Guide)

From HM Revenue & Customs · COTAX Manual

To understand the common period rules when reallocating from tax to penalty or interest whether or not the receiving Accounting Period (AP) is a Quarterly Instalment Payment (QIP) case, follow steps 1 to 6.

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1. Is the Effective Date of Payment (EDP) of the payment later than today’s date? If yes, go to step 2 If no, go to step 3 2. The EDP of the RTO posting is set to the EDP of the payment. 3. Is the normal due date of the donating AP which you are reallocating from later than today’s date? If yes, go to step 2 If no, go to step 4 4. The EDP of the posting is set to today’s date. Is the normal due date of the donating AP which you are reallocating from later than the EDP of the payment? If yes, go to step 5 If no, go to step 6 5. Repayment interest is due on the donating AP which you are reallocating from, for the period from the normal due date +1 to today’s date. 6. Repayment interest is due on the donating AP which you are reallocating from for the period from the payment’s EDP +1 to today’s date.