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HMRC internal manual

VAT Default Interest Manual

Interest adjustments: Completion of Form VAT663

To complete a VAT663 you will need to get a copy of the current interest calculation record (ICR) for the relevant assessment, see VDIM5000. If the amendment is particularly complex or if you have any queries on the effect processing the VAT 663 may have, you should consult Tax Administration, Litigation and Advice (TALA), see VDIM1040.

Some or all of the following fields will need to be completed depending on how the form is to be used:

Registration Number - This is a nine-digit number, which is the trader’s unique identification within the VAT system.

OA Reference Number - The reference number of the original OA to which the Interest adjustment is to be made (eleven digits).

Form Indicator - A single numerical digit with a value of 0 to 5 indicating the type of adjustment.

0 - reduce tax liable amount,

1 - increase tax liable amount,

2 - reduce Default Interest,

3 - increase Default Interest,

4 - reduce Further Interest,

5 - increase Further Interest.

Event Value - An eleven-digit number, nine in pounds plus pence.

  • If the Form Indicator to be used is 0 or 1, the amount of the tax adjustment (i.e. the amount from which interest is to be withdrawn or imposed) to be placed on the ICR table.
  • If the Form Indicator to be used is 2 or 3, the amount of interest to be adjusted on the OA Default Interest.
  • If the Form Indicator to be used is 4 or 5, the amount of further interest to be adjusted on the OA Further Interest.

Start Date - The date in six-digit format (DDMMYY) from which interest is to stop or start being calculated on the tax amount in the event value field. If however the amount in the event value field is interest or further interest to be reduced or imposed, enter 999999.

End Date - The date in six-digit format (DDMMYY) of the day after the tax adjustment is to end. However if a direct interest adjustment is involved the end date will automatically set to 000000 when the start date equals 999999.


If a bulk assessment has been processed the interest bearing tax (IBT) will be incorrect as the computer cannot calculate interest on these. You will need to increase the IBT by imposing interest between specific dates on the under declaration line processed as a 00/00 period, but you will only be able to do so if another under declaration has been processed on the same VAT641/642. Otherwise you will need to calculate the interest manually, applying the 3 year limit as appropriate. To assess interest on a bulk assessment (period 00/00) you should complete the VAT 663 as follows:

Registration number

OA reference number

Event value - Insert the amount of tax on which interest is to be assessed.

Start date - Insert the date from which you want interest to start being calculated on the amount in the event value. This will be the later of the earliest start date on the Interest Calculation Record, see VDIM5100, or 3 years back from the calculation date, see VDIM2040 on the VAT assessment.

End date - Insert the date of the day after you want the adjustment to end.