20. An applicant's applicable amount is the aggregate of each of the following amounts which apply in the applicant's case—
(a)an amount in respect of the applicant's personal allowance, determined in accordance with paragraph 2 of Schedule 1;
(b)an amount in respect of any child or young person who is a member of the applicant's family, determined in accordance with paragraph 3 of Schedule 1 (personal allowances);
(c)if the applicant is a member of a family of which at least one member is a child or young person, the amount specified in paragraph 4 of Schedule 1 (family premium); and
(d)the amount of any premium which may be applicable to the applicant, determined in accordance with Parts 3 and 4 of Schedule 1 (disability premiums).