Emergency Tax Code W1: Why It Follows You and How to Escape
An emergency tax code W1 can quietly drain your pay for months. Here's exactly why it gets applied, what it costs you, and how to get HMRC to remove it.
Your first payslip from a new job arrives and something looks wrong. The tax deduction is higher than you expected, and next to the tax code there are two letters: W1. That suffix is not a clerical quirk. It is HMRC putting your employer on notice to treat every single pay period as though it stands alone, disconnected from the rest of the tax year. The result, in most cases, is that you overpay tax every month until someone takes action. That someone will not be HMRC.
- The W1 suffix means your tax is calculated week by week, not cumulatively across the tax year, which almost always causes overpayment.
- HMRC applies W1 automatically when it lacks enough information about your income history, usually at a job change or after a gap in employment.
- Your employer cannot remove W1 on their own initiative. You must contact HMRC directly, or use your Personal Tax Account online.
- Once HMRC issues a corrected cumulative tax code, your employer will automatically refund any overpaid tax through your next payslip.
- Leaving W1 in place for a full tax year means you may not receive an automatic refund. You would need to claim it manually.
What the W1 Suffix Actually Does to Your Tax
- Emergency Tax Code W1
- An emergency tax code carrying the suffix W1 (Week 1) instructs an employer to calculate income tax on each week's pay in isolation, without reference to how much tax has already been paid earlier in the tax year. The equivalent for monthly-paid employees is M1 (Month 1). Both operate on a non-cumulative basis, meaning the personal allowance is applied only to that single pay period rather than spread across the whole year.
Under a standard cumulative tax code such as 1257L, your employer's payroll software tracks every pound you have earned since 6 April and every pound of tax you have already paid. If you were on sick leave for six weeks, your cumulative unused allowance builds up and your next payslip reflects that, often resulting in a lower deduction or even a refund within the payroll run itself.
W1 strips all of that away. Each week is treated as week one of a brand new tax year. Your £12,570 personal allowance for 2025-26 is divided by 52, giving you a weekly slice of approximately £241.73. Any earnings above that are taxed at the relevant rate. Last week's figures are irrelevant. The month before that is irrelevant. Every pay period resets to zero.
For someone earning £40,000 a year, paid monthly, the difference is not trivial. Under a correct cumulative 1257L code, your monthly tax-free portion is around £1,047. Under M1 (the monthly equivalent of W1), it is the same figure, so far so good. The problem emerges when your earnings are uneven, when you had a gap between jobs, or when you started mid-year with no P45. In those cases, a cumulative code would carry forward your unused allowance. W1 or M1 simply ignores it.
Why HMRC Puts You on W1 in the First Place
HMRC does not apply W1 to cause you inconvenience, though it manages to do so anyway. The code is applied because HMRC genuinely does not know enough about your income history to trust a cumulative calculation. Specifically, W1 tends to appear in four situations.
Starting a new job without a P45. When you leave an employer, they are required to issue a P45 summarising your earnings and tax paid to date. If you lost it, never received it, or simply started a job before the P45 arrived, your new employer has no data to feed into payroll. HMRC issues a temporary code, almost always with W1 or M1 attached.
Starting your first ever job. If you have never been employed in the UK before, there is no tax history for HMRC to reference. W1 applies by default until you confirm your situation through a starter checklist.
Returning from a long break. If you were out of employment for a significant period, perhaps caring for a family member or recovering from illness, HMRC may be uncertain whether you have received other taxable income during the gap. W1 is the cautious holding position.
Multiple income sources flagged. If HMRC believes you have more than one employer or a secondary income stream, it may apply a restricted or emergency code with W1 to one or all sources while it works out the correct allocation of your personal allowance.
The common thread is uncertainty. W1 is HMRC's way of saying: "We are not confident enough in your year-to-date position to let the cumulative calculation run freely." The problem is that it then falls entirely to you to supply the missing confidence.
The Real Cost: A Worked Example
Take Jamie, an electrician employed by a contractor. He left his previous firm in November, took three months off over winter, and started a new role in February. His new employer never received a P45 (Jamie's old firm was slow to issue it), so payroll put him on 1257L W1.
Jamie earns £3,500 per month gross. Under W1, his tax-free monthly slice is £1,047.50 (£12,570 ÷ 12). His taxable income each month is £2,452.50, generating a tax bill of around £490. Over three months to the end of the tax year on 5 April, that is £1,470 in tax.
But Jamie only worked for five months in total that year (November plus February, March, and April at the new job). His actual annual income was approximately £17,500. His real tax liability for the year, after applying the full £12,570 personal allowance, should have been roughly £980. He overpaid by around £490, money that sat with HMRC instead of in his bank account.
If Jamie does nothing, HMRC may issue a P800 reconciliation after the tax year closes. That process has its own delays and complications, as we covered in detail in our post on the P800 Tax Calculation Refund. But Jamie does not have to wait. He can act now.
How to Fix an Emergency Tax Code W1: Step by Step
Fixing a W1 code means persuading HMRC to replace it with a cumulative code and giving your employer the updated information. There are three routes.
Route One: Your Personal Tax Account (Fastest)
Log into your Personal Tax Account at gov.uk/personal-tax-account. Under "PAYE Income Tax", you can view your current tax code and see which employer it applies to. If the code shows W1 or M1, you can update your employment details, confirm your income from previous sources, and request a code change directly through the interface. HMRC typically issues a revised code within a few days, which is then sent electronically to your employer's payroll software.
This is the quickest route for most people, and it is free. You can also check your tax code for free at /check-my-tax-code to confirm exactly what code is currently in force before you start.
Route Two: Call HMRC Directly
The income tax helpline is 0300 200 3300, open Monday to Friday, 8am to 6pm. Have your National Insurance number ready, along with details of your previous employer (or confirmation that you had no previous employment this tax year). HMRC will update your record during the call and issue a new code notice (a P6) to your employer.
Calls can be long. HMRC's own performance data shows average wait times regularly exceeding 20 minutes during peak periods (typically January to April). If you can use the Personal Tax Account instead, do.
Route Three: Submit a Starter Checklist
If you have not yet given your new employer any information about your previous employment, ask their payroll team for a starter checklist (formerly the P46). This form asks three key questions about whether you had a P45, whether this is your only job, and whether you have received any other income this tax year. Your answers directly determine whether W1 is appropriate.
If you tick the box confirming this is your only job and you have not received any other taxable income since 6 April, your employer is required to apply a cumulative code. The starter checklist does not go to HMRC directly. It instructs your employer's payroll, who then report to HMRC through Real Time Information (RTI). HMRC will confirm or adjust the code based on what it receives.
What Happens Once HMRC Issues a Corrected Code
When HMRC removes the W1 suffix and issues a cumulative code (for example, changing 1257L W1 to simply 1257L), your employer's payroll software will run a cumulative calculation at the next pay run. It will total up everything you have earned since 6 April, calculate what your tax liability should have been across that entire period, subtract what you have already paid, and the difference will be refunded through your payslip. You do not need to fill in a separate refund form. You do not need to wait until after the tax year. The correction is automatic and immediate.
This is worth emphasising because many people assume tax refunds require a separate claim. For PAYE employees, the moment the code is corrected, the overpayment flows back through payroll. See our related post on Wrong Tax Code Refund: How Much Can You Actually Claim? for a fuller breakdown of the refund process and timelines.
What If the Tax Year Has Already Ended?
If you reach 5 April still on a W1 code, the cumulative correction no longer applies automatically. The tax year has closed. Your employer's payroll software cannot go back and recalculate.
In this case, HMRC should issue a P800 tax calculation in the months following the end of the tax year, typically between June and November. If you overpaid, the P800 will confirm the amount and give you instructions to claim a refund online through your Personal Tax Account. The refund is paid directly to your bank account, usually within a few weeks of the claim.
If you do not receive a P800 but suspect you overpaid, you can contact HMRC directly to request a review of the closed tax year. The four-year rule applies: you can claim back overpaid tax for up to four previous tax years. For 2025-26, that means claims back to 2021-22 are still valid.
You may also want to check your tax code free at /check-my-tax-code to see whether previous years were affected and whether a backdated claim is worth pursuing.
People also ask
The Bit HMRC Does Not Advertise
There is a structural reason why W1 codes persist longer than they should. HMRC relies on Real Time Information, the system by which employers report payroll data to HMRC every time they pay an employee. When RTI works, HMRC knows your year-to-date earnings almost instantly and can issue an updated code quickly. When it does not, because a previous employer submitted late, because there was a gap in reporting, or because you had no prior PAYE record, the system defaults to caution. The W1 suffix is that caution made operational.
What HMRC does not proactively tell you is that you are the one who needs to break the deadlock. There is no automatic trigger that says: "This person has now been on W1 for three months; we should probably sort this out." The onus is entirely on the employee to notice, to investigate, and to act. For someone who gets one payslip a month and does not scrutinise the tax code line, W1 can run for an entire tax year without correction.
If you have been reading about why your tax code looks unusual, our post on Tax Code on Your Payslip: What Each Part Actually Means explains the full anatomy of a UK tax code and what every letter and number signifies.
For context on what a correctly functioning tax code should look like, Tax Code 1257L in 2025-26: What Your Payslip Isn't Saying covers the standard code that most employees should see and what it actually guarantees (and does not guarantee) in terms of tax accuracy.
One Last Thing Before Your Next Payslip
Remember the question from the opening: something looks wrong on your payslip. The W1 code is the answer, and now you know exactly what to do about it. Log into your Personal Tax Account, confirm your employment history, and request the code correction today. If your next pay run is within a week or two, you may well see the overpayment refunded before the month is out.
Do not leave it to HMRC to notice. They will not. Check your current tax code at /check-my-tax-code and make sure every pay period from here is calculated correctly.
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