IHTM31185 - Raising assessments: IOP(WIR) assessment

The assessment is the same as for the ordinary IOP assessment ( IHTM31184), except that interest is charged differently to take into account the interest relief ( IHTM30363).

COMPASS should calculate interest at

• box 1 on the unpaid tax from the due date of the last instalment to the Effective Date ( IHTM31187) of the assessment
• box 2 does not apply
• box 3 on 1/10 of the change in tax from the second due date to the third, 2/10 from the third due date to the fourth and so on, up to the latest due date.

As you can appreciate, the calculation of interest with interest relief is not straightforward and COMPASS often gets this wrong, particularly where the tax charge is apportioned between property on which instalments apply and which they don’t.

Always check the interest charge calculated by COMPASS. If you need to make any adjustments you can do this in the relevant Adjustment box.