Emergency Tax Code: Why You Have One and How to Change It

An emergency tax code is a temporary code your employer or pension provider uses when HMRC hasn’t confirmed the right one for you. It ends in W1, M1 or X, and it taxes each pay period on its own instead of across the whole tax year. That usually means paying too much tax until the code is corrected.

Your first payslip from a new job lands, the number is smaller than the offer letter suggested, and there’s a stray M1 sitting after your tax code. That’s an emergency tax code.

Nothing has gone wrong exactly: HMRC didn’t have enough information about your income to work out a proper code before payday, so your employer used a stand-in.

The system that produces the code is the same one that fixes it. Employers report pay to HMRC every time they run payroll, and a corrected code follows once HMRC can see the full picture.

What varies is how long that takes, and whether the overpaid tax comes back through your salary or sits with HMRC until the tax year ends.

What follows covers what the W1, M1 and X suffixes do to your pay, why the code turns up in situations unrelated to starting a job, how long it should last, and how to claim back an emergency tax code overpayment.

How an emergency tax code changes your pay

A normal tax code is cumulative. Your employer looks at everything you’ve earned since 6 April, everything you’ve already paid in tax, and how much of your tax free personal allowance you’ve used, then works out this month’s deduction so the running total stays right.

An emergency tax code throws that history away. Each pay period is treated as though it’s the first of the year, which is why you’ll also see it called a non-cumulative tax code, a month 1 tax code or a week 1 tax code.

You do still get your personal allowance. That’s the part most explanations get wrong. On 1257L M1 you receive one twelfth of the personal allowance each month, or one fifty-second of it each week on 1257L W1. For 2026/27 that allowance is £12,570. What you lose is the benefit of any allowance you didn’t use earlier in the year.

Picture someone starting a job in September on £30,000, having earned nothing since April:

• On a cumulative 1257L code, six months of unused allowance can be set against that first payslip, so no tax comes out of it at all.
• On 1257L M1, only one month’s allowance applies, and the rest of that month’s pay is taxed at 20%.
• The gap closes later, but only once HMRC issues a cumulative code or the tax year ends.

Your own figures will differ, so treat that as an illustration rather than a calculation of your position. The direction is the point: an emergency tax code front-loads your tax bill.

W1, M1 and X all mean the same thing

The suffix tells payroll which pay frequency applies, not how much tax you’ll pay. All three do an identical job:

• A W1 tax code applies when you’re paid weekly.
• An M1 tax code applies when you’re paid monthly.
• An X tax code applies when your pay dates follow neither pattern, four-weekly for example.

Depending on the payroll software you may see NONCUM printed instead of a suffix, which GOV.UK treats the same way.

The emergency tax code list is therefore shorter than it looks. 1257L W1, 1257L M1 and 1257L X are the same code applied to three payroll cycles. In Scotland and Wales the number carries a prefix, giving S1257L and C1257L with the same suffixes attached.

Two other codes get called emergency codes and aren’t quite the same thing. A BR tax code taxes everything from that source at the basic rate with no allowance at all, and a 0T tax code (a zero, not the letter O) removes the allowance and applies tax across every band.

Both can be entirely correct on a second job or a pension, which is set out in what a BR tax code means for your pay.

If your code reads 1257L with nothing after it, it’s cumulative and none of this applies to you. The detail behind the number sits in how the 1257L tax code is calculated.

Your starter checklist answer sets your first code

Where there’s no P45, the HMRC starter checklist does the job instead. The starter checklist tax code your employer runs from your first payday depends entirely on which of three statements you tick:

• Statement A produces a cumulative 1257L code, for a first job since 6 April with none of the taxable benefits the form lists.
• Statement B produces 1257L W1 or M1, where this is now your only job but you had another job or one of those benefits earlier in the year.
• Statement C produces a BR tax code, for a second job or a pension alongside existing employment.
• No checklist at all leaves your employer using 0T, which gives no allowance and, for a basic rate taxpayer, the same result as BR.

That last line is the one to act on. An emergency tax code new job situation is uncomfortable enough without landing on 0T as well, so completing the form on your first day is the single thing genuinely within your control.

A P45 tax code from the current year does the job faster still, because your new employer can carry over both the code and your figures to date. An emergency tax code without P45 details is simply the fallback when that isn’t possible.

The trap runs the other way too. Ticking statement A on a genuine second job feels harmless, and it isn’t: you claim the full allowance twice and owe the difference later. Statement C is the right answer there, however small the earnings.

Emergency tax codes are not only for new jobs

Changing employer is the obvious trigger and far from the only one. Your code turns provisional whenever your income changes faster than HMRC’s records do:

• Moving from self-employment into PAYE work leaves your new employer with no previous PAYE record to work from.
• Beginning to draw the State Pension adds taxable income that has to be set against your allowance.
• Picking up a taxable benefit like a company car changes your allowance part way through the year.
• Taking on a second job more often produces a BR code than a W1 or M1 one, because your allowance is already used elsewhere.

In each case the PAYE tax code isn’t wrong so much as provisional. HMRC issues it on the information available and refines it once payroll data catches up.

Company benefits deserve a note of their own. A company car reduces your allowance for as long as you have the car, and if HMRC’s figures are out of date the code stays wrong long after the emergency suffix has gone.

Pension withdrawals are taxed as if they repeat

The largest overpayments don’t come from payroll at all. They come from the first time someone takes money flexibly out of a pension.

Providers work to the same rules as employers, but the numbers get much bigger. Without a current P45 or a code from HMRC, the provider applies an emergency code, and the calculation assumes your withdrawal repeats every month for the rest of the year. Take £10,000 as a one-off and it’s taxed as though £120,000 is on the way, pushing money you were never going to receive into higher bands.

The tax comes back. Which route depends on what you did with the pot:

• P55 covers a partial withdrawal where the pot isn’t emptied, no further payments are due that tax year, and the provider cannot make the refund itself.
• P53Z covers an emptied pot where you still have other taxable income.
• P50Z covers an emptied pot where you’ve also stopped working.
• P53 covers a trivial commutation of a pension fund, or a small pension taken as a lump sum.

Each form has a guide in the income tax forms section.

Submit the right form and HMRC works out the repayment and pays it by Faster Payments, then checks the figures again after the tax year ends.

Do nothing and the money still comes back, but not until that year-end reconciliation, which can mean waiting months for tax you never owed. GOV.UK sets out what each claim needs in its guidance on reclaiming tax after a flexible pension payment.

One caveat for higher earners: an emergency tax code pension deduction doesn’t always overtax. In some cases it collects too little, and the balance falls due later.

An emergency tax code is meant to be temporary

HMRC updates your code once both your old and new employers have reported. For a job change, GOV.UK guidance on emergency tax codes puts that at up to 35 days from the day you start. In straightforward cases the trigger is automatic: your employer reports your pay, HMRC matches it to your record, and a new code goes out to both of you.

Two things stretch that timeline.

The first is missing information at your end. Where no P45 arrived and no starter checklist was completed, HMRC has nothing to work from and the clock hasn’t really started.

The second is where your change in circumstances has left you underpaid for the year. GOV.UK is clear that the emergency code stays until you have, which can mean carrying it through to 5 April.

So how long does emergency tax last in practice? Weeks rather than months when the paperwork is in order, and potentially the rest of the tax year when it isn’t.

Check your tax code before the next payday

Your code sits on every payslip, usually near your National Insurance number. It also appears on your P60, on any P45, and in your personal tax account.

Looking online tells you more than the payslip does. Your personal tax account tax code breakdown shows how HMRC built the figure, so you can see which benefit or income source moved your allowance. The HMRC app shows the same detail.

What to look for:

• A W1, M1 or X after the number means an emergency code is running.
• A code that doesn’t match your circumstances points to a wrong tax code rather than an emergency one, which is a different problem with a different fix.
• A coding notice you don’t recognise repays reading in full, because it lists every adjustment HMRC has applied.

Where the breakdown doesn’t match your situation, HMRC’s tax code online service lets you update the details directly.

A tax code checker explains what each part of the code means if the notice isn’t clear. It takes a few minutes and costs nothing, which is a reasonable trade against paying too much tax for six months.

Claiming back an emergency tax code overpayment

How you get the money back depends on when the code is fixed and which tax year the overpayment falls in.

If the code is corrected during the tax year

Corrected inside the same tax year, the money usually returns through payroll. Your new cumulative code recalculates the year to date, and the refund shows up as a smaller deduction on your next payslip rather than a separate payment. No claim, no form.

If you stop working before the year ends

Stopping work part way through leaves no payroll to refund you. Form P50 claims the money back before 5 April rather than after it.

The conditions GOV.UK sets are four weeks or more out of work without taxable state benefits, retirement with no pension from your old employer, no expectation of going back to work, or a return to full-time study. Your final pay has to have gone through, and you need parts 2 and 3 of your P45.

Several near-identical situations need something else. A new job inside four weeks means your next employer repays you through your salary, an occupational pension means the provider does it, and pension withdrawals go on the forms above.

If the claim waits until after 5 April

HMRC reviews your record after the tax year ends and issues a P800 tax calculation where you’ve over or underpaid. The P800 sets out the figures and explains how to claim, and it repays checking against your own payslips first.

How fast it arrives depends on the route: five working days for an online claim, around six weeks for a cheque you request, and fourteen days from the letter date where one comes automatically.

Earlier years work the same way, up to a point. To claim back emergency tax from a previous year, your claim has to reach HMRC within four years of the end of the tax year the overpayment arose in. Miss that and the year closes, so an emergency tax code refund nobody chased eventually stops being recoverable.

Keep your payslips for the period either way, so HMRC’s figures can be checked against what was actually deducted. An emergency tax rebate isn’t a favour or a windfall, it’s your own money coming back.

What to do next

An emergency tax code is a placeholder, not a penalty. It taxes each pay period in isolation, which usually means too much comes out until HMRC holds enough information to issue a proper code.

Most of the fix is administrative. Hand over a P45 or complete a starter checklist accurately, check what your payslip and personal tax account actually say, and let payroll reporting do the rest. Where a pension withdrawal is involved, the reclaim forms shorten a wait that would otherwise run to the end of the tax year.

If the code looks wrong rather than temporary, working through the tax codes guides is a sensible step before taking it up with HMRC.

Key Takeaways

• An emergency tax code ends in W1, M1 or X, and taxes each pay period on its own rather than across the tax year.
• You keep your personal allowance on 1257L W1 or M1, but only a slice of it per pay period, which is why the deductions look high.
• Giving your employer a P45, or completing a starter checklist accurately, is the fastest route off an emergency code.
• HMRC guidance says a new-job code update can take up to 35 days from your start date, and the emergency code runs to 5 April where an underpayment is still outstanding.
• First pension withdrawals are taxed as though the payment repeats monthly, and forms P55, P53Z, P50Z and P53 reclaim the excess during the tax year.
• Overpaid tax returns through payroll in-year, or after HMRC’s year-end check via a P800 tax calculation, and a claim for a past year must reach HMRC within four years of that tax year ending.

Common emergency tax code questions

The questions below sit alongside the main routes off an emergency code, and the answers follow HMRC guidance and standard payroll practice.

What happens if you change jobs again before the code is corrected?

Your P45 does the work. When you leave, your employer issues one showing the tax code in use along with your pay and tax to date, and your next employer works from parts 2 and 3 of that form.

An emergency code sitting on a P45 is not a problem in itself. What matters is that the year to date figures travel with you, because those are what let a cumulative code be applied once HMRC issues one.

Where the job ends before any P45 arrives, the starter checklist covers the gap at the next employer. A second emergency code is a real possibility, but the overpaid tax stays on your record either way and is picked up when HMRC reconciles the year.

Does an emergency tax code affect National Insurance?

No. National Insurance is worked out separately from income tax and doesn’t use your tax code at all.

Contributions are calculated on your earnings in each pay period, against weekly or monthly thresholds, and on each job independently rather than on your combined annual income. That calculation runs identically whether your code is cumulative or has an M1 after it. Company directors are the exception, because their contributions are worked out on annual earnings rather than pay period by pay period.

The practical upshot is that a first payslip under an emergency code shows inflated income tax and normal National Insurance. If the NI figure also looks wrong, the cause lies elsewhere, perhaps your category letter or a payroll error.

What if an employer keeps using the emergency code after HMRC issues a new one?

Employers have to operate the code HMRC sends them and can’t change a code on request. The instruction arrives as a coding notice, and payroll applies it from the next available pay run.

Timing explains most cases. A notice issued after payroll has been processed won’t take effect until the following period, so one more payslip under the old code is normal rather than a fault.

Where several pay periods pass with no change, the gap usually sits between HMRC and the employer rather than at the employer’s end. Your personal tax account shows which code HMRC believes is in force, and that’s the information needed before raising it with either party.

Can an emergency tax code carry over into a new tax year?

The suffix shouldn’t, though the code itself often does. GOV.UK states that where an emergency code has run to the end of a tax year, you should be on a non-emergency code from the start of the new one, because the year’s tax has by then been settled. In practice your employer often keeps the same code number and simply drops the suffix, so each pay period stops being taxed in isolation. The number stays; the isolation goes.

What can carry over is the underlying problem. If HMRC still lacks the information that caused the emergency code, the replacement may also be wrong, just without the W1 or M1 marker on it.

Tax overpaid in the earlier year doesn’t disappear either. It sits on your record until HMRC’s year-end review picks it up or until you raise it, which is why it pays to look back at older payslips when an emergency code ran for several months.

Does an emergency tax code change student loan repayments?

No. Student loan deductions are calculated on gross pay above your plan’s repayment threshold, and they don’t reference your tax code.

Both deductions land on the same payslip, which is what makes a first payslip hard to read. Income tax may be inflated by the emergency code while the student loan figure is entirely correct, and the two need looking at separately.

One point to know if you’ve recently graduated: repayments don’t begin until the tax year after your course finishes, so a deduction appearing earlier than that is a separate issue from your tax code and worth querying with payroll.