Emergency tax code explained: what it is, what it costs you, and how to fix it (UK 2026/27)

What is an emergency tax code?

An emergency tax code is a temporary code HMRC operates when they do not yet have a complete picture of your year-to-date earnings. It is a holding pattern, not a punishment. You usually end up paying a little more tax for a month or two, and the system corrects itself once HMRC catches up.

The most common situation is starting a new job without handing your new employer a P45 from the previous one. Without that handover document, your new employer has nothing to tell HMRC what you have already earned and what tax you have already paid this tax year. So HMRC plays it safe.

How to spot an emergency tax code on your payslip

The tax code is printed near the top of your payslip, usually alongside your gross pay or National Insurance number. An emergency code shows up in one of two ways:

• A suffix of W1, M1, or X after a normal-looking number, for example 1257L W1 or 1257L M1. The W1/M1 marker tells you the code is non-cumulative.
• A flat code with no number, such as BR, 0T, D0, or D1. These do not apply a personal allowance at all and tax your whole pay at a flat rate.

A plain 1257L on its own (no W1, no M1, no X) is the standard cumulative code and not an emergency code. You can read more in our guide to tax code 1257L.

The four emergency tax codes you will see

We cover the 0T code in detail in our 0T tax code guide if HMRC has put you on that specifically.

Why W1/M1 matters: a worked example

Say you start a new job in October (month 7 of the tax year) on a salary of £36,000. You had not worked at all earlier in the tax year. With cumulative 1257L, your first October payslip would give you 7 months of personal allowance against your first month of pay, so you would pay almost no tax.

With 1257L W1/M1, the system only gives you 1 month of allowance against 1 month of pay. The maths becomes:

• Monthly gross: £3,000
• Monthly allowance: £1,047 (one-twelfth of £12,570)
• Taxable: £1,953 at 20% = £390.60 income tax

On a cumulative code you would have paid around £100 in tax that month. So W1/M1 has cost you about £290 extra in October alone. The good news is you get all of it back through the following payslip once HMRC reconciles your record. The bad news is that until they do, your cash flow is squeezed for a month or two.

The five reasons HMRC puts you on an emergency code

1. You started a new job and did not hand over a P45. This is by far the most common cause. The P45 carries your year-to-date earnings, tax paid, and previous tax code. Without it, HMRC has nothing to feed into PAYE.
2. You finished your first ever job. A first employer often runs emergency code at the start because you had no previous PAYE record to base a normal code on.
3. You came back to the UK after working abroad. Your new employer files RTI; HMRC matches you to your old NI record; you go cumulative within a pay cycle or two.
4. You took on a second job or pension. The second payer is typically issued a BR or 0T code while HMRC decides which employer should hold your personal allowance.
5. You returned from a long career break or maternity leave. Same mechanism as a new job, your previous employer handed back your record when you left, so HMRC waits for fresh data before issuing a normal code.

How long an emergency code usually lasts

One to two pay periods in most cases. The flow looks like this:

1. You start a new job on, say, 6 October.
2. Your employer pays you on 25 October and files Real Time Information (RTI) to HMRC the same day.
3. HMRC receives the RTI feed, matches it to your National Insurance number, and pulls up your full earnings record.
4. HMRC issues a coding notice (P6) to your employer within 2 to 4 weeks. Your employer applies the new code from the next pay run.
5. On the next payslip, the cumulative code recalculates your year-to- date tax. Any excess deducted under W1/M1 is refunded straight into that payslip.

If you are still on an emergency code after two complete pay periods, it is worth contacting HMRC. The two most common reasons for delay are: your previous employer has not closed off your record correctly, or HMRC has a missing or duplicated NI number on file.

How to fix an emergency tax code, three routes

1. Personal Tax Account (fastest)

Log in at gov.uk/personal-tax-account using Government Gateway credentials. You can see your current code, all sources of income HMRC has on file, and request a code change inline. HMRC usually issues a corrected code to your employer within 3 to 5 working days. This is the route we recommend for almost every client.

2. Phone HMRC

Call 0300 200 3300 (Monday to Friday, 8am to 6pm). Have your National Insurance number and a recent payslip ready. Useful if your Personal Tax Account is not yet set up or if your situation is unusual (overlapping employments, recently arrived from abroad, pension on top of salary).

3. Self Assessment

If you file a Self Assessment return anyway, your tax position is reconciled at year-end through that return. Any tax overpaid through PAYE comes back to you as part of the SA balance. This is the fall-back route if the emergency code only persisted for a month or two and was fixed automatically before you got around to logging in.

Will I get the overpaid tax back automatically?

In most cases, yes. When HMRC moves you from a W1/M1 basis to cumulative 1257L, the next payslip applies year-to-date numbers and refunds any overpayment as part of that pay run. You do not have to claim it.

The exceptions where you may need to take action:

• You left the job before HMRC fixed the code. The refund follows you to your next PAYE job, or is settled through Self Assessment at year-end. If neither applies (for example, you stopped working entirely), you can claim the refund directly using form P50 on gov.uk.
• You stopped working part-way through the tax year. If you have left employment and do not expect to work again before 5 April, you can claim a refund of overpaid PAYE without waiting for year-end.
• HMRC issued the wrong cumulative code. If your new code is technically not emergency but still wrong (e.g. it includes a benefit you no longer receive), you still need to request a review.

What to do this week if you have just spotted one

• Take a screenshot of your payslip. You will want the code and date as evidence if anything has to be escalated.
• Hand over the P45. If you started a new job and still have not given them your P45, do it today. Most cases resolve from that single step.
• Fill in the Starter Checklist if you do not have a P45 to hand. Your employer should give you one; the form is also available on gov.uk. Tick the right statement carefully (A, B, or C) because that statement drives which emergency code your employer uses.
• Set up a Personal Tax Account if you do not have one. It pays for itself in time saved the next time anything goes wrong with PAYE.
• Give it one pay period. Most emergency codes self-correct within 4 weeks once your employer has filed RTI.

When emergency tax becomes a Self Assessment issue

For most employees, emergency tax is a short-term PAYE issue that resolves itself. For people who file Self Assessment (sole traders, landlords, company directors, higher earners), there are two extra considerations:

• SA reconciliation, your final tax for the year is calculated from total income across all sources. Any over- or under-payment through PAYE is folded into the SA balance. You will not be left out of pocket.
• Payments on account, HMRC bases your January and July payments on account on your prior-year liability. A year with an unusual PAYE pattern can throw these off, leaving you paying too much or too little upfront. Worth flagging to your accountant if you have had a job change mid-year.