Emergency Tax Calculator UK

Emergency tax is applied when HMRC doesn't yet have enough information about your income, often when starting a new job without a P45. It typically uses your standard Personal Allowance but calculates tax non-cumulatively for each pay period, which can result in paying more tax than you ultimately owe.

Common reasons include starting a new job without giving your employer a P45, starting a second job, receiving company benefits not yet reflected in your tax code, or returning to work after a gap. Your employer uses an emergency code until HMRC sends updated instructions.

Usually yes. If you've overpaid tax due to an emergency code, this is typically corrected automatically in later pay periods once HMRC issues your correct tax code, or via a refund after the tax year ends if you've left a job. You can also contact HMRC directly to query an overpayment.

Emergency tax codes usually only last until HMRC receives full details of your income and issues an updated, correct tax code to your employer — often within a few pay periods. Providing your P45 or completing a new starter checklist promptly helps speed this up.

These are all variations of emergency tax codes calculated non-cumulatively: W1 is used for weekly paid employees, M1 for monthly paid employees, and X is used when the exact pay frequency basis is unclear. All apply your Personal Allowance to that single pay period only, rather than spreading it across the year.

Give your new employer your P45 from your previous job as soon as possible, or complete the HMRC starter checklist accurately if you don't have a P45. This gives HMRC the information needed to issue your correct, cumulative tax code promptly.