P45What it means, in plain English

A P45 is the form an employer must give an employee when they stop working for them. It shows the employee's tax code and their pay and tax deducted so far in the current tax year, which runs from 6 April to 5 April. The new employer uses it to apply the right tax code from the first payday; without it, the starter completes a starter checklist and may initially be taxed on an emergency code.