Updating Your Tax Code

You may be put on an emergency tax code if you change jobs. HM Revenue and Customs (HMRC) will correct it automatically after you’ve given your employer details of your previous income or pension.

Your employer will get these details from your P45 – if you don’t have one, they should ask you for further information.

HMRC will also update your tax code when:

After your tax code changes

HMRC will adjust your tax code so you pay the right amount of tax across the year. They’ll write to you or email you when your tax code has been updated.

They will also tell your employer or pension provider that your tax code has changed. Your next payslip should show:

  • your new tax code
  • adjustments to your pay if you were paying the wrong amount of tax

Find out more here

Understanding W1 or M1 Tax Codes

If your employee’s tax code has ‘W1’ or ‘M1’ at the end

W1 (week 1) and M1 (month 1) are emergency tax codes and appear at the end of an employee’s tax code, eg ‘577L W1’ or ‘577L M1’. Calculate your employee’s tax only on what they are paid in the current pay period, not the whole year.

Updating for the new tax year

HM Revenue and Customs (HMRC) will tell you between January and March about any new tax codes to use for employees in the new tax year. This starts on 6 April.

If an employee’s tax code isn’t changing, HMRC won’t contact you and you should carry forward the employee’s tax code to the new tax year.

If your employee’s tax code ends with ‘M1’ or ‘W1’ (‘month 1’ or ‘week 1’), don’t carry this part of the code into the new tax year.

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