Emergency tax codes: W1, M1 and X

How to spot an emergency code

GOV.UK says you are on an emergency tax code if your tax code ends in W1 (used when you are paid weekly, for example 1257L W1), M1 (used when you are paid monthly, for example S875L M1) or X (used when your pay dates vary, for example C663L X). You could also see NONCUM on your payslip, depending on your employer's payroll software.

GOV.UK says that if your tax code does not end in W1, M1, X or NONCUM, you are not on an emergency tax code.

GOV.UK lists W1 as an emergency tax code.

GOV.UK lists M1 as an emergency tax code.

GOV.UK lists X as an emergency tax code.

GOV.UK lists NONCUM as an emergency tax code.

What it does to your tax

Tax is usually worked out on your total income so far in the tax year. On an emergency tax code it is worked out on what you are paid in that week or month only, as if you were paid that amount every week or month of the year. GOV.UK says this could mean you pay the wrong amount of tax.

GOV.UK's guidance for employers says W1 (week 1) and M1 (month 1) are emergency tax codes that appear at the end of a tax code, for example 577L W1 or 577L M1, and that the employer works out tax only on what is paid in the current pay period, not the whole year.

GOV.UK's guidance for employers says 1257L is an emergency tax code only if it is followed by W1, M1 or X, and that emergency codes can be used if a new employee does not have a P45.

A new job

If a new employer does not have your previous income and tax details, you are paid using an emergency tax code. GOV.UK says this is usually temporary.

If you start a job and your new employer does not know your previous income details, GOV.UK says you may be put on an emergency tax code.

GOV.UK says that giving the P45 from your previous job to your new employer gives them your details and can help take you off the emergency tax code. If your previous employer did not give you a P45, you can ask them for one.

HMRC will usually update your tax code when it gets all your details from your new and previous employers, and send the code to you and your new employer. GOV.UK says this can take up to 35 days from when you start your job.

If you started a job more than 35 days ago and think your tax code is still wrong, GOV.UK points to its page on how to update your tax code.

GOV.UK says that if you have started a new job, it advises waiting 35 days for HMRC to get your new income details before contacting HMRC.

Benefits and the State Pension

GOV.UK says you might be put on an emergency tax code if you start getting company benefits or the State Pension. It says this is normal and helps you pay the right amount of tax for that tax year.

GOV.UK says you can check your tax code online to make sure it includes the company benefit or State Pension. If they are not included, you can update your details in the tax code online service or by contacting HMRC.

In the case of company benefits or the State Pension, GOV.UK says you will have an emergency tax code until the end of the tax year, and in the new tax year you will be put on a non-emergency tax code.

Too much or too little tax

GOV.UK says that if you have not paid enough tax, you stay on the emergency tax code until you have paid the correct tax for the year, and that if you have paid too much tax you can get a tax refund.

If you are on the wrong tax code, GOV.UK says you may pay too much or too little tax. You can get a refund or pay the tax you owe once HMRC has your income details for the tax year.

If you have paid too much tax, GOV.UK says that when HMRC updates your tax code it checks whether it has all your income details for the tax year. If it does, it works out the difference and asks your employer or pension provider to refund it in your pay, which usually happens when they use your new tax code.

If you have not paid enough tax, GOV.UK says HMRC will estimate how much tax you owe when your tax code is updated, adjust your tax code to collect the tax over one or more tax years if possible, and check your tax after the end of the tax year and send you a letter if you have not paid the right amount. It adds that you will have an emergency tax code until the end of the tax year, and a non-emergency tax code in the new tax year.

After the tax year

After the end of the tax year, HMRC gets income details from employers, pension providers and the benefits office. GOV.UK says HMRC will then check how much tax you have paid, send you a letter if you have not paid the right amount, let you know how to get your refund if you have paid too much, and update your tax code if needed.

If you have paid too much or too little tax by the end of the tax year (5 April), GOV.UK says HMRC will send you either a tax calculation letter (also known as a P800) or a Simple Assessment letter, which tells you how to get a refund or pay tax you owe.

GOV.UK says these letters are sent out between June and March of the following tax year.

If you think the amounts used in your tax calculation are wrong, GOV.UK says you can contact HMRC and tell it which amounts you think are incorrect and what they should be.

If the code looks wrong

HMRC usually updates your tax code using information it gets from your employer or pension provider. GOV.UK says that if your tax code is wrong, it is usually because HMRC has incorrect or missing information, and that to correct it you check and update the details HMRC has about you.

GOV.UK says using the online service is the quickest way to check and update your details: sign in to the Check your Income Tax online service, check your employment, pension, estimated taxable income, company benefit and expenses details, and update your details if there is anything wrong or missing.

If you think your tax code is wrong and you cannot use the online service, GOV.UK says you can contact HMRC. HMRC's Income Tax enquiries line is 0300 200 3300. The Income Tax enquiries line is open Monday to Friday, 8am to 6pm, and closed on bank holidays.

• Tax code notice (P2)The letter HMRC sends when your code changes

GOV.UK pages on this

• GOV.UK: Emergency tax codesGOV.UK's page on emergency tax codes: the endings, what they do to your tax and how a new job is sorted out.
• GOV.UK: If you think your tax code is wrongGOV.UK's page on what to do if you think your tax code is wrong.
• GOV.UK: If you have paid too much or too little taxGOV.UK's page on what happens if you have paid too much or too little tax.
• GOV.UK: Tax overpayments and underpaymentsGOV.UK's guide to tax overpayments and underpayments, including the P800 tax calculation letter.

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