Starting a New Job? Emergency Tax Codes Cost Real Money

Starting a new job on Monday is exciting. Seeing 'W1' or 'M1' stamped on your first payslip is not.

An emergency tax code is HMRC's way of saying: "We don't know enough about you yet, so we'll tax you as if you have no history." For many new starters, that translates directly into an overpayment on their very first pay day. If you're earning £35,000, that first month on an emergency code could mean paying roughly £200 more in tax than you should. Welcome to the new job.

What Is an Emergency Tax Code?

The standard personal allowance for 2024/25 and 2025/26 is £12,570, which gives most employees the tax code 1257L. Under a normal cumulative code, your employer spreads that allowance evenly across every pay period in the year. If you start a new job in October, midway through the tax year, your employer's payroll software will take into account that you've already used (or preserved) five months' worth of allowance.

Add the W1 or M1 suffix and all of that context disappears. Your employer treats each week or month as if it stands alone, with no reference to what came before. You get one-twelfth of your annual allowance for that month and no more. Any unused allowance from previous months is invisible to the calculation.

For a new starter who was unemployed for the first half of the tax year, this matters enormously.

Why Do New Starters Get Emergency Codes?

There are three main triggers, and none of them require any mistake on your part.

Your P45 was late or missing

When you leave an employer, they are supposed to issue a P45 immediately. In practice, it often arrives days or weeks after your start date at your new employer. Without it, payroll cannot confirm your previous earnings or the tax you've already paid this year. The safest option for the employer, legally speaking, is to apply an emergency code and wait.

You completed the starter checklist incorrectly

Since April 2013, HMRC replaced the P46 with a new starter checklist. You tick one of three statements: this is your first job since leaving full-time education (statement A), you have another job or pension (statement B), or you've had a job or claimed benefits since last April (statement C). Each statement maps to a different starting tax code. Tick the wrong box in a rush on your first morning and your code could be wrong from day one.

HMRC's systems haven't caught up

Even when everything is submitted correctly, HMRC's PAYE Real Time Information (RTI) system sometimes takes time to issue the correct code to your new employer. Until that notification arrives, your employer defaults to the emergency basis. This is not incompetence on anyone's part. It is a structural feature of how RTI operates.

The Real Cost: A Concrete Example

Sarah is a project manager earning £3,000 per month. She started a new job in September, having been between jobs since May. Her new employer cannot locate her P45 on her first day, so payroll assigns her the code 1257L M1.

Under M1, she receives one-twelfth of her £12,570 personal allowance: £1,047.50 for September. Her taxable pay is £3,000 minus £1,047.50, or £1,952.50. Tax at 20% comes to £390.50.

Under a correct cumulative code, her employer would recognise that she had no income from May to August and had preserved four months of unused allowance. Her cumulative allowance by September would be around £6,285. Her taxable year-to-date pay would be just £3,000 minus £6,285, which is negative, meaning zero tax owed in September and a credit carried forward.

The difference in that single month is roughly £390. Over a few months before the code is corrected, it compounds. Sarah is not doing anything wrong. She is simply a new starter caught by a timing gap in HMRC's systems.

How to Check if You're on the Wrong Code Right Now

Your tax code appears on every payslip, usually as a number followed by a letter or letters. If you see W1, M1, or 0T on your current payslip, that is a red flag.

• 1257L W1 or 1257L M1: Emergency basis. You may be overpaying.
• 0T: No personal allowance applied at all, typically a rate of 20% on all earnings. This is the most aggressive emergency code and can result in significant overpayment.
• BR: Basic rate across all pay, usually a sign of a second-job code applied to your main job by mistake.

If you're unsure, check your tax code for free at /check-my-tax-code now. It takes less than sixty seconds and tells you immediately whether the number you see on your payslip matches what HMRC should have issued.

You can also log into your HMRC Personal Tax Account at gov.uk. Your current tax code is displayed there, alongside the reason HMRC has issued it.

How to Fix an Emergency Tax Code

The good news is that this is one of the more straightforward tax problems to resolve. You have two routes.

Route 1: Contact HMRC directly

Call HMRC's income tax helpline on 0300 200 3300 (Monday to Friday, 8am to 6pm). Have your National Insurance number and your new employer's PAYE reference to hand. HMRC will update their records and issue your employer a new tax code, usually within a few days. Your payroll will apply the correction in the next pay run.

Alternatively, use the HMRC Personal Tax Account online to update your employment information. This is often faster than waiting on hold.

Route 2: Provide your employer with your P45

If you have your P45, give it to payroll immediately. They can input the figures directly and switch you from emergency to cumulative. This is the fastest resolution if the P45 exists and your previous employer issued it correctly.

If you have lost your P45 or your previous employer has not issued one, your employer cannot simply take your word for your previous earnings. In that case, Route 1 (contacting HMRC) is the only option.

Will HMRC Refund the Overpaid Tax Automatically?

This is where many new starters get frustrated. The short answer is: eventually, but not reliably, and not necessarily on your timetable.

If your emergency code is corrected during the same tax year, the cumulative calculation in payroll software will trigger a refund through your pay automatically. Once your employer switches you to a cumulative 1257L, the next payroll run will calculate your tax-to-date on all earnings since April, compare it to what you have actually paid, and credit the difference in your next pay packet. No forms required.

If the tax year ends before the code is corrected, you will need to reclaim the overpayment separately. HMRC may issue a P800 tax calculation in the autumn following the tax year end, which identifies the overpayment and initiates a refund. But P800s are not guaranteed to reach everyone who is owed money, and the timeline stretches well into the following year.

The lesson: do not wait and assume HMRC will sort it. Act now.

The Starter Checklist: The Part Most People Rush

If you don't have a P45 (perhaps you were previously self-employed, or you're starting your first PAYE job, or too much time has passed since your last role), your employer will ask you to complete a starter checklist. The three statements are deceptively simple.

Statement A: This is your first job since 6 April and you have not been receiving taxable Jobseeker's Allowance, Employment and Support Allowance, taxable Incapacity Benefit, a State Pension, or an occupational pension.

Statement B: This is now your only job but since 6 April you have had another job, or you have received taxable Jobseeker's Allowance, Employment and Support Allowance, or taxable Incapacity Benefit.

Statement C: As well as your new job, you have another job or pension.

Statement A generates a cumulative 1257L code. Statements B and C generate emergency (W1/M1) codes by default. If you're in a genuine Statement A situation but tick B out of confusion, you will be over-taxed immediately. Read it carefully. It is worth a few seconds of your first day.

If you have multiple income sources or a side business alongside your new employment, you may also want to read Self Employed and PAYE: Why Your Tax Code Is Probably Wrong, which covers the specific problems that arise when HMRC tries to balance two income streams through one code.

What If You've Been on an Emergency Code for Several Months?

If you started a job earlier this tax year and have only just noticed the W1 or M1 on your payslip, do not assume the overpayment is written off. As long as you are still in the same tax year (which runs from 6 April to 5 April), a corrected cumulative code will trigger an automatic refund through payroll.

Step one: check your current code at /check-my-tax-code. Step two: If it still shows W1, M1, or 0T, call HMRC today. Step three: Confirm with your employer's payroll team that they have received the updated code before the next pay run.

For a detailed walkthrough of whether your code is correctly formed, the Verify Tax Code Accuracy UK: A Forensic Checklist covers every element of a tax code in sequence. It is a useful second step once you've confirmed the basic emergency suffix issue.

If you're thinking about whether the same problem could affect a current code that has no emergency suffix but still looks wrong, Is My Tax Code Correct? How to Check in 60 Seconds is a fast starting point.

One Final Point About Timing

The tax year ends on 5 April. If you are reading this in March and you started a job in September still on an emergency code, you have weeks, not months, before the window for an in-year automatic refund closes. After 5 April, the resolution process becomes slower and requires HMRC to issue a P800 or for you to initiate a formal reclaim.

That first payslip with W1 stamped on it was not your fault. The structural gap between leaving one employer and HMRC updating the next is a known, documented feature of the PAYE system. But the correction will not happen unless you push for it.

Check your code. Ask for what you're owed.

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