An emergency tax code is a temporary code applied by HMRC when they lack details about your previous income, usually after starting a new job. It usually ends in W1, M1 or X. It is normally used when your full tax history is not yet available.
If you understand how the system works, it is much easier to spot whether you are on the wrong code and what to do next.
In this guide, you will get to know in detail:
- What is an emergency tax code?
- How do I know if I’m on an emergency tax code?
- How do emergency tax codes work
- And much more…
Let’s break it down!
What Is an Emergency Tax Code?
An emergency tax code is a temporary PAYE tax code. It is used by HMRC when they do not yet have enough information to calculate your correct Income Tax.
Rather than delaying your wages, your employer continues to deduct tax using temporary rules. They do this until they receive the correct information.
Emergency tax codes are a temporary measure. HMRC usually updates your tax code once they have more information about your income.
How Do Emergency Tax Codes Work?
Normally, the UK uses a cumulative tax system. Under that system, your tax-free allowance is divided into twelve monthly parts or fifty-two weekly parts. If you do not use your allowance in month one, it rolls over into month two. This helps keep your tax deductions more accurate across the year.
Another important point to remember is that the employers do not choose emergency tax codes themselves. They follow the tax code provided by HMRC or payroll starter procedures until updated information is received.
What an emergency code does is stop this rolling process completely. This is because it applies a non-cumulative tax basis. Under this system, every month stands alone. You get exactly one-twelfth of the Personal Allowance for that single month.
If you had a gap between jobs where you earned nothing, that unused allowance is temporarily ignored. This means you will miss out on the immediate tax relief for those blank months. Yes, until your code is updated back to a cumulative basis.
What Is the Difference Between Cumulative and Non-Cumulative Tax Codes?
To fully understand how do emergency tax codes work, you need to understand the difference between cumulative and non-cumulative tax codes.
The fundamental difference between a cumulative and a non-cumulative tax code is how your tax-free Personal Allowance is applied throughout the financial year.
A cumulative tax code calculates your tax based on your total earnings and tax paid since the start of the tax year. A non-cumulative code means your tax is calculated using only your current pay period (that specific week or month). Basically, it completely ignores your total earnings and also tax paid earlier in the tax year.
Cumulative vs Non-Cumulative Tax Codes: Summary
| Feature | Cumulative Tax Code (Standard) | Non-Cumulative Tax Code (W1 / M1 / X) |
| History Check | Yes. Looks at total year-to-date earnings and tax paid. | No. Treats the current week or month in total isolation. |
| Unused Allowance | Rolls over to the next month to lower your future tax. | Is completely frozen and cannot be used in that pay period. |
| Fluctuating Income | Automatically adjusts your tax if your pay goes up or down. | Taxes you as if you earn that exact amount every single month. |
| Likelihood of Overpaying | Low (keeps your tax accurate month-by-month). | High (often results in too much tax being deducted). |
What Do W1, M1 and X Mean?
If your tax code ends in W1, M1 or X, you are on an emergency tax code.
- W1 means your tax is worked out weekly,
- M1 means monthly, and
- X is used when your pay dates vary.
You may also see NONCUM on a payslip. This actually depends on the payroll software your employer uses.
W1, M1, and X all mean the same basic thing that HMRC is taxing the payment on a non-cumulative basis. And therefore, the current pay run is looked at on its own.
If your tax code does not end in W1, M1, X or NONCUM, that simply means you are not on an emergency tax code.
Why Might HMRC Assign an Employee to an Emergency Tax Code?
HMRC assigns an employee to an emergency tax code when they do not have enough
up-to-date information about the worker’s income to issue a precise, permanent code.
There are a few common reasons to be on an emergency tax code. This includes:
1. You started a new job without a P45 from your previous employer
This is by far the most common reason to put an individual on an emergency tax code. When you leave a job, your old boss gives you a P45. A P45 shows the employee’s total earnings and the amount of tax deducted during the current tax year. If you do not hand this to your new employer before your first payday, they of course have to guess your tax status.
2. You went from self-employment to a PAYE role
If you were working for yourself and have now taken an employed role, you do not have a P45 to hand over. As a result, the system defaults to an emergency setting until things clear up.
3. You have multiple jobs
If you take on a second job or a side gig, HMRC might apply an emergency or BR tax code to that second income. This is to avoid giving you the Personal Allowance twice over.
4. Company benefits changed
If you suddenly get a company car, private healthcare, or start receiving the State Pension, HMRC might apply a temporary code. Yes, while they work out how much your allowance should drop.
How Do I Know If I’m on an Emergency Tax Code?
You can find out if you are on an emergency tax code by checking your most recent payslip. Your tax code is usually printed next to your National Insurance number, payroll ID, or tax calculations.
If your code is showing 1257L W1, 1257L M1, 1257L X, BR or OT, it usually indicates you are on an emergency code. Codes such as BR or 0T may sometimes be used temporarily when HMRC does not yet have complete information, although they can also be permanent tax codes in some situations.
You can also check your tax code through your Personal Tax Account on GOV.UK. You can check it via the HMRC app too.
If you are unsure, you can call HMRC on 0300 200 3300.
It’s also worth knowing that BR and OT tax codes can also serve as emergency tax codes. A BR code taxes every single penny at 20% without giving you any tax-free allowance at all. An 0T code also means you have no tax-free Personal Allowance. It taxes you across the 20%, 40%, and 45% bands. This depends on how much you earned that month.
So it is not always just W1 or M1 to watch for.
How Long Does an Emergency Tax Code Stay in Place?
An emergency tax code typically stays in place until HMRC receives your correct details. Or, at most, until the end of the current tax year.
The exact duration depends entirely on how quickly HMRC receives the required missing income data. Officially, HMRC often update tax codes within 35 days of an employee starting a new job, although processing times vary. But in some cases, people can stay on an emergency code for longer than they should.
If you have not paid enough tax, you will stay on the emergency tax code. And in case you have paid too much, you can get a tax refund.
If you think your tax code is still wrong, you can update it. For that, you can use the tax code online service or contact HMRC directly.
Remember that you should not assume that it will resolve itself. You must keep an eye on your payslips every month. And also check your Personal Tax Account if you are not sure where things stand.
How Do I Claim Back Emergency Tax?
How you claim back overpaid emergency tax depends entirely on whether you are still working at that job and when the emergency tax was deducted.
1. If you are still in the job
If you are still in the job, then you usually do not need to do anything complex. Once your employer receives your P45 or you complete a Starter Checklist, they send the data to HMRC. Then, HMRC will issue a revised tax code to your employer via an electronic notice.
And on your very next payday, the cumulative system comes into effect. It will automatically calculate what you should have paid since April and compare it to what you actually paid. It then refunds the difference directly into your pay or bank account.
You will see a negative tax figure or a lower tax deduction than usual on your payslip.
2. If you leave the job before the tax year ends
If you stop working partway through the year (for example, a student finishing a summer job) and you also do not plan to work again before 5th April, you do not have to wait. Yes, you can simply log into your Personal Tax Account on GOV.UK and fill out Form P50. This way you can claim your money back instantly.
3. If the tax year has already ended
If the tax year closes on 5th April and you are still owed money, the employer cannot refund you through payroll. Instead, HMRC will look at all your income data over the summer.
They will send you a P800 tax calculation letter. HMRC normally sends these letters between June and November following the end of the tax year. Furthermore, this letter will state exactly how much you overpaid. You can then log into your Personal Tax Account on the GOV.UK website to claim the refund directly into your bank account. You can also check it using the HMRC app.
When Might You Get an Emergency Tax Code on Pension Withdrawals?
You get an emergency tax code on a pension withdrawal if:
- It is your first time taking money from that pension.
- You make a one-off cash withdrawal instead of a regular monthly income.
- You do not give the provider a recent P45 form.
This is because the system mistakenly assumes you will take this exact same amount every month. And this causes the system to overcharge you. It means you will pay too much tax. Then you will have to claim it back from HMRC.
Quick Summary – Emergency Tax Code
- An emergency tax code is temporary and usually ends in W1, M1 or X
- It means your tax is calculated per pay period, not across the full year
- The most common cause is starting a new job without a P45
- Pension withdrawals almost always trigger emergency tax on the first payment
- You may be entitled to a tax refund if too much tax has been deducted.
- You have four years to claim back any overpaid tax before the right lapses
- Checking your tax code early can prevent months of incorrect deductions.
The Bottom Line
The emergency tax code exists because the PAYE system needs a starting point when information is missing. It is not a penalty, and it is not permanent. But it can mean you hand over more money than you owe.
The key is not to ignore it. Check your payslip, look at your tax code, and if you see W1, M1 or X, you need to take action.
Submit your P45, complete your Starter Checklist, or use the GOV.UK reclaim forms if it relates to a pension. The emergency tax code usually results in any overpaid tax being refunded once HMRC updates your records.
How Accotax Can Help
At Accotax, we deal with tax code issues like this regularly, for employees, self-employed individuals, and people managing pension drawdown for the first time.
If you have been placed on an emergency tax code and are not sure whether you have overpaid or underpaid, we can review your position quickly and clearly.
Disclaimer: The information about “What Is the D0 Tax Code? And How Does It Affect Your Earnings in 2026/27?” is provided in this article including text and graphics. It does not intend to disregard any of the professional advice.
