You must make sure HMRC receives your completed form within 28 days of the end of the quarter in which the car benefit change you're reporting took place. The four end-of-quarter dates are:
5 July
5 October
5 January
5 April
Make sure that any P46 (Car) forms relating to the quarter ended 5 April are submitted before the P11D forms for the same tax year to avoid confusion and which may lead to incorrect notices of coding being issued.
