When you start a new job without giving your employer a current-year P45, you complete a Starter Checklist (the modern replacement for form P46). The checklist asks you to pick one of three statements, each of which results in a different starter tax code:
Statement A - 'this is my first job since 6 April and I have not received any taxable benefits or pension': you get the standard 1257L cumulative tax code. Statement B - 'this is now my only job, but since 6 April I have had another job, or received taxable jobseeker's allowance, etc., and I do not get a state pension': you get 1257L Week 1/Month 1. Statement C - 'I have another job or receive a state or occupational pension': you get the BR (basic rate, 20%) code on the new job's earnings, with the personal allowance still applied at the original employer.
The wrong statement is one of the most common causes of overpaid PAYE - picking C when B was correct, for example, will tax all your new job's earnings at 20% from £1, generating a hefty refund position by year-end.
Worked example: Tariq leaves Employer A in February 2026 and starts at Employer B in April 2026. He doesn't have his P45 yet because Employer A has been slow. Statement A is incorrect because he has had earnings since 6 April. Statement B is the right pick: he gets 1257L M1, paying tax conservatively until either his P45 arrives or HMRC issues a coding notice based on his RTI history. Until Tariq either gets a P45 or contacts HMRC to switch to cumulative, he may overpay tax for several months - his recovery route is the year-end P800 reconciliation or a mid-year call to HMRC requesting a cumulative code.
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