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HMRC internal manual

COTAX Manual

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

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

1. Is the 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 AP from which you are reallocating 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 AP from which you are reallocating 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 AP from which you are reallocating for the period from the normal due date +1 to today’s date.
6. Repayment interest is due on the AP from which you are reallocating for the period from the payment’s EDP +1 to today’s date.