The Kept Pound UK take-home pay calculator

Guide · Published 31 October 2026

Emergency tax codes: what they mean and how to fix them

If your tax code ends in W1, M1 or X, you're on an emergency tax code. It's common, especially when you start a new job, and any tax you overpay comes back to you. Codes like 0T and BR aren't officially emergency codes, but employers often use them for the same reason: they don't have your details yet.

Codes to look out for

Code on your payslipWhat it means
1257L W1, 1257L M1 or 1257L X (emergency codes)You get the standard allowance, but only a week's or month's share each pay period. Payroll doesn't look back at earlier in the tax year. Some payroll software shows this as NONCUM.
0TNo tax-free allowance at all, so all your pay is taxed. Employers use this when you've given them no starter information.
BRAll pay taxed at the 20% basic rate, with no allowance. This is normal for a second job or a pension alongside a job, but wrong if it's your only income.

W1 and M1 stand for "week 1" and "month 1": each pay period is treated as if it were the first of the tax year. X does the same thing. In Scotland the codes start with an S, such as S1257L M1 or S0T.

Why you've been given one

When you start a job, the starter checklist asks you to pick one of three statements. Choosing A (this is your first job since 6 April) normally gets you the full 1257L code. B (this is your only job now, but you've had another since April) gets 1257L on a W1/M1 basis. C (you have another job or a pension) gets BR. If you don't give your employer any information, they have to use 0T.

How much it costs you

Take someone earning £30,000 a year, paid £2,500 a month, in their first month of the tax year:

Normal code (1257L)Emergency 0T
Gross pay£2,500.00£2,500.00
Income tax£290.20£500.00
National Insurance£116.16£116.16
Take-home pay£2,093.64£1,883.84

That's about £210 less that month. National Insurance isn't affected by your tax code. With a W1 or M1 code the monthly difference is smaller, but it can build up over the year. If you had months earlier in the year with no income, a W1/M1 code won't give you the allowance from those months until it's fixed.

How to fix it

  1. Give your employer your P45 from your last job, if you have it.
  2. Fill in the starter checklist if you haven't, and make sure you've picked the right statement.
  3. Check your code in your HMRC online account or the HMRC app. You can see each employer's code there and update your details, for example to tell HMRC an old job has ended.
  4. Contact HMRC if the code is still wrong after a couple of pay days. Your employer can't change the code themselves. They can only use what HMRC sends them.

After you start a new job, HMRC usually updates your code within 35 days. If it's still wrong after that, you can update it yourself online.

Getting your money back

Once you're moved onto a normal code, payroll looks back over the whole tax year, and any tax you've overpaid is usually refunded in your next payslip. If the year ends before that happens, HMRC works it out after 5 April and sends you a P800 tax calculation. That explains how to claim the refund online, so it can be paid straight into your bank account.

Two jobs?

If you have more than one job, your allowance normally goes on your main job, and the second one uses BR. If your main job pays less than £12,570, you can ask HMRC to split your allowance between the two, so you don't overpay through the year.

See how a tax code changes your take-home pay.

Try it with code 0T

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