Section 143 | Deduction for periods when car unavailable
From legislation.gov.uk
(A1)This section has effect for the purposes of—F1
(a)section 121(1) (method of calculating the cash equivalent of the benefit of a car), andF1
(b)section 121B(1) (optional remuneration arrangements: meaning of “modified cash equivalent”).F1
(1)A deduction is to be made from the amount carried forward from step 6 of section 121(1) or (as the case may be) step 4 of section 121B(1) if the car has been unavailable on any day during the tax year in question.F2
(2)For the purposes of this section a car is unavailable on any day if the day—
(a)falls before the first day on which the car is available to the employee,
(b)falls after the last day on which the car is available to the employee, or
(c)falls within a period of 30 days or more throughout which the car is not available to the employee.
(3)The amount of the deduction is given by the formula—F3
Formula
where—
U is the number of days in the year on which the car is unavailable,
Y is the number of days in that year, and
A is the amount carried forward from step 6 of section 121(1) or (as the case may be) step 4 of section 121B(1) .
(4)This section is subject to section 145 (modification where car temporarily replaced).