What Is Emergency Tax? Definition and How It Works

If your first payslip from a new job shows a far smaller net pay than you expected, emergency tax is almost certainly the culprit. HMRC's default position when it lacks the right information is to deduct more, not less, which means you effectively lend the government money interest-free until the situation is resolved.

Why Emergency Tax Happens in the First Place

The root cause is always an information gap. HMRC's PAYE system works by instructing your employer which tax code to use. That code tells your employer how much of your salary to protect from tax each pay period. When there is no instruction, your employer must use an emergency code as a fallback.

The most common triggers are:

• Starting a new job without a P45. If you cannot hand over a P45 from your previous employer, your new payroll team has no record of how much you have already earned or paid in tax that year.
• Starting your first ever job. HMRC has no prior employment record to work from.
• Taking a first flexible pension withdrawal. Pension providers routinely apply emergency tax to the first lump sum drawn under pension freedoms, sometimes dramatically overtaxing it (more on this below).
• Returning to work after a gap. If your last employer has not yet filed updated information with HMRC, the system treats you as unknown.

The Two Emergency Codes and What They Actually Do

Understanding which emergency code you are on matters, because they behave differently and produce different levels of overtaxation.

Code 1257L W1/M1: The Week-One or Month-One Basis

The W1/M1 emergency tax code is the most frequently applied. The "1257" part is the same numeric value as the standard Personal Allowance for 2025/26, so at first glance it looks fine. The problem is the W1 or M1 suffix, which switches your tax calculation from cumulative to non-cumulative.

A normal cumulative code considers everything you have earned and paid since 6 April. A W1/M1 code treats each pay period in isolation, as if it were the very first week or month of the tax year. This means you cannot benefit from any unused allowance built up earlier in the year, and you cannot have previous overpayments corrected automatically. You pay a flat slice of tax each period with no running total to balance things out.

Code 0T: Zero Allowance, Maximum Pain

The 0T tax code is harsher. It grants you no Personal Allowance at all. Every pound of your earnings is taxed from the first penny, at the relevant rate bands: 20% basic rate, 40% higher rate, 45% additional rate. HMRC typically applies 0T when it has no information whatsoever and needs a conservative (aggressive) default, or when a previous employer has used up your allowance record in a confusing way.

For a basic-rate taxpayer earning around £35,000 a year, being on 0T for a full month rather than the correct cumulative 1257L code could mean roughly £1,000 extra deducted from a single payslip.

A Worked Example: First Pension Withdrawal

Pension emergency tax is where the overtaxation can be startling. Suppose you are 57, a basic-rate taxpayer, and you withdraw £20,000 as your first flexible lump sum from a defined-contribution pension.

The pension provider has no cumulative earnings data for you. Under the emergency basis, it effectively annualises that single payment, treating it as if you will receive £20,000 every month for the rest of the tax year, which projects to an annual income of £240,000. It then deducts tax at the rates that would apply to that annualised figure.

You are not taxed incorrectly forever; the overpayment comes back. But it can take weeks or months unless you use HMRC's specific pension tax reclaim forms (P55, P53Z or P50Z depending on circumstances).

How to Fix Emergency Tax Quickly

The fastest resolution is almost always to supply the missing information:

1. Hand over your P45. Give it to your new employer's payroll team as soon as possible. They will submit the figures to HMRC and your code should correct within one or two pay periods.
2. Complete a starter checklist. If you have no P45, your employer will ask you to fill in a starter checklist (previously called a P46). Answer the questions accurately; your answers determine whether they apply Statement A, B or C, which affects the code used while HMRC catches up.
3. Contact HMRC directly. Call 0300 200 3300 or use your Personal Tax Account online. HMRC can issue a revised code to your employer immediately in many cases.
4. Check your code yourself. You can check your tax code online via HMRC's tool to see exactly which code is live and whether it has already been updated. Do not wait for your employer to tell you; look for yourself.

Once HMRC issues the correct code, your employer's payroll software recalculates cumulatively. Any tax you overpaid earlier in the year is automatically credited back through future payslips in the same tax year. If the tax year ends before the correction is made, HMRC will issue a P800 tax calculation and refund you directly.

Emergency Tax and Self-Employed People

If you are a sole trader operating entirely through Self Assessment, emergency tax in the PAYE sense does not touch you. Your income tax bill is calculated once a year on your tax return, and you pay it by 31 January. There is no employer deducting from your invoices.

However, you can still be hit by emergency tax if you:

• Also hold an employed position alongside your self-employment. The employed income goes through PAYE and can trigger all the same emergency code issues.
• Draw income from a pension while running your business. The pension provider applies emergency tax just as it would for anyone else.
• Start employment after a period of self-employment, because HMRC may not have a current P45 or clear cumulative earnings record to pass on.

If you use Making Tax Digital software or a platform like TapTax to track your self-employed income, it will not prevent emergency tax on a separate PAYE income, but keeping accurate records means you can spot a coding error quickly by comparing what should have been deducted against what actually was.