IHTM30361 - Interest period: general rule
In most cases interest runs from the day after the due date (IHTM30151) to the date of payment. The due date for payment is determined by the type of charge to tax and there is more detail at pages IHTM30151 - 30156.
There are some exceptions to this general rule and details can be found elsewhere in this section (IHTM30371).