The supplementary charge: increase of relief for decommissioning expenditure where it is taken into account for PRT purposes: the amount of additional deduction
The additional deduction given in computing the adjusted ring fence profits is an amount equal to the appropriate fraction of the PRT difference.
The appropriate fraction is equal to (SC-20%)/SC, where SC is the rate of supplementary charge for the relevant accounting period. With a supplementary charge rate of 32% the appropriate fraction is 3/8ths.
The PRT difference is the difference between the amount of PRT due for the chargeable period (which may be nil) and the amount of PRT which would be due for that chargeable period if the decommissioning expenditure were not taken into account for PRT purposes.