Emergency Tax Code Explained, What It Is and How to Fix It

What an emergency tax code actually is

An emergency tax code is a temporary code your employer applies when HMRC cannot confirm your correct tax position, usually because you have started a new job without providing a P45, or because HMRC does not yet hold information about your income. The most common emergency code is 1257L W1/M1. The '1257L' part means your personal allowance is treated as £12,570, which is correct, but the W1 (week 1) or M1 (month 1) suffix means you are taxed on a non-cumulative basis.

Non-cumulative means the payroll system ignores any tax you have already paid in the current tax year. Instead of spreading the annual allowance and thresholds across the whole year and catching up on any previous underpayment or overpayment, it treats each pay period as if it is the first of the year. If you started in month 8, you will have used none of your personal allowance from months 1–7, so your first payslips on emergency tax should not drastically over-deduct, but other emergency codes that do not include the personal allowance (like 0T) will over-deduct significantly.

The '0T' code is particularly harsh. It applies no personal allowance at all and taxes all earnings from pound one. On a £3,000 monthly salary, that means income tax of roughly £600 per month instead of the expected £287, a difference of over £300 per month. This is the code most likely to cause the dramatic over-deductions people report when starting a new job.

• 1257L W1/M1: personal allowance applied, but non-cumulative (most common emergency code).
• 0T: no personal allowance, significant over-deduction risk.
• BR: basic rate on everything, typically used if you have a second income source.
• Emergency codes usually appear on your first payslip from a new employer.

Why you end up on emergency tax and who is most affected

The most common trigger is starting a new job without handing over a P45. Your P45 is a form your previous employer gives you when you leave. It tells HMRC and your new employer what you earned and how much tax you paid in the current tax year, which allows your new employer to calculate cumulative tax correctly from day one.

Students starting their first job, people returning to work after a break, and anyone who lost their P45 are the most common casualties. Agency workers are also frequently affected, especially on short-term assignments where paperwork moves slowly. The system automatically generates emergency codes rather than guessing, which is the right policy, it just results in over-deduction for the employee until the position is corrected.

If you are on more than one job simultaneously, your secondary employer is supposed to use a BR or D0 code (taxing at 20% or 40% with no allowances) because your personal allowance should be claimed on the primary job. Emergency coding on a second job is therefore less of a problem, but it does mean you need to ensure your primary employer is applying the allowance correctly.

• No P45 from your last job is the most common cause.
• First job ever, HMRC has no record of a previous employer.
• Return to work after a career break.
• Starting a second job alongside existing employment.

How to fix it, and get a refund

The fastest route is to contact HMRC directly. You can do this via your Personal Tax Account at gov.uk, through the HMRC app, or by calling the income tax helpline on 0300 200 3300. You will need your National Insurance number, your payroll number or PAYE reference, and details of your current employer. HMRC will update your tax code and issue a new one to your employer, usually within a few days.

Once the correct code is applied, most payroll systems will automatically calculate any overpaid tax from earlier in the year and refund it through your pay, this happens automatically in the same tax year because cumulative PAYE catches up. If you are owed a refund near the end of the tax year (after 5 April), you may need to claim it directly through Self Assessment or an R40 form.

If you cannot reach HMRC and you need to give your employer something to work with, you can fill in a 'Starter Checklist' (formerly called a P46) which your employer uses to apply an interim code. It asks whether this is your only job and whether you have been in employment recently, the answers determine which code gets applied before HMRC confirms the right one.

• Contact HMRC via gov.uk Personal Tax Account, quickest resolution.
• Have your NI number and employer PAYE reference ready.
• Overpaid tax within the year is usually refunded automatically via payroll.
• Post-year-end refunds may need a P800 check or direct claim.