UK emergency tax codes explained: what W1, M1, X, 0T and BR mean and how to reclaim overpaid tax

If more tax came out of your first pay packet in a new job than you expected, you have probably been put on an emergency tax code. It is a temporary code used when your employer does not yet have full details of your income for the year. Here is what codes like W1, M1, X, 0T and BR mean, why you end up on one, and how to reclaim any overpaid tax through your Personal Tax Account with HMRC.

What is an emergency tax code?

It is a temporary code used while your employer or pension provider has no record of your income and the tax you have already paid since the start of the tax year. The UK tax year runs from 6 April 2026 to 5 April 2027. The usual code for someone with one job is 1257L, which gives the standard tax-free Personal Allowance of £12,570 a year. An emergency code either removes that allowance or works it out in a restricted way.

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Which codes are emergency codes — W1, M1, X, 0T?

Your code is an emergency code if it ends in W1, M1 or X:

• W1 if you are paid weekly (for example 1257L W1);
• M1 if you are paid monthly (for example S875L M1);
• X if your pay dates vary (for example C663L X).

Some payslips show NONCUM instead, depending on the payroll software. Separately, the code 0T is used when your Personal Allowance has been used up, or when you have started a new job and your employer does not have the details they need to give you a code. The code BR means all income from that job or pension is taxed at the basic rate, with no tax-free allowance, which is common on a second job or pension.

Why have I been put on one?

Usually because you have changed jobs. If your new employer does not know your income and the tax you have already paid, they put you on an emergency code until the picture is complete. Give them the P45 from your last job to help remove it. If you have no P45, ask your previous employer for one or fill in a starter checklist. You might also be put on an emergency code when you start getting company benefits or the State Pension, which is normal.

How does it affect my pay?

Normally your tax is based on your total income so far in the year. On an emergency code it is based only on what you are paid in the current week or month, as if you earned that amount every period of the year. That can mean the wrong amount of tax, and often too much. If you have paid too little, you stay on the emergency code until the correct tax for the year is paid.

How do I fix the code and get a refund?

Start by checking your code online. After a job change, HMRC usually updates your tax code within up to 35 days of your start date. If it has been more than 35 days and the code still looks wrong, follow the GOV.UK guidance on how to update your tax code. If you have overpaid, you can claim a tax refund. The easiest route is the Check your Income Tax for the current year service: it shows your code and Personal Allowance, lets you update your income, employer or pension details, and lets you tell HMRC about changes that affect your code. You sign in through your Personal Tax Account or the HMRC app, and you may need to prove your identity, usually with photo ID. If a company benefit or the State Pension is missing, add it there or contact HMRC. The full rules are on the GOV.UK emergency tax codes page.