A premium payable by an employer to which section 430(1) applies but was not registered under section 434 during a part of a premium period is to be calculated in accordance with the relevant premiums order and this Part and the formula—
where—
P is the premium or portion of the premium payable for the part of the premium period in respect of which the employer was not registered under section 434;
D is the amount of premium payable for the full premium period calculated in accordance with the premiums order for the premium period;
E is the number of days in the premium period during which the employer was not registered under section 434;
F is the number of days in the premium period during which the employer was an employer to which section 430(1) applies.