Understand Your Payslip, Tax Code and PAYE / Lesson 4 of 8
Emergency codes and why they happen
First payslip in a new job, and the tax looks enormous. Here is why.
The short answer
- ✓ Emergency codes are non-cumulative: each period is treated as the first
- ✓ W1, M1 and X after your code are the markers
- ✓ They usually overtax you, and the money comes back when the code goes cumulative
- ✓ Completing the starter checklist is the fastest way to avoid one
What an emergency code is
An emergency code gives you the standard personal allowance but applies it on a non-cumulative basis. Each pay period is treated as though it were the first of the year, so nothing you earned earlier is taken into account.
You will see it written as your code followed by W1, M1 or X.
| Marker | Meaning |
|---|---|
| W1 | Week 1 basis, for weekly payrolls |
| M1 | Month 1 basis, for monthly payrolls |
| X | Either, depending on the payroll |
Why it usually overtaxes you
Because each period stands alone, you get one month's worth of allowance each month and no credit for allowance you did not use earlier. Someone who starts a job in September has eight months of unused allowance that an emergency code simply ignores.
Cumulative code allowance available so far 6/12ths, so tax is low
Emergency code allowance available 1/12th only
Same salary, same month, materially different deduction.
The difference comes back once the code goes cumulative.What triggers it
- Starting a job without giving your employer a P45
- Starting your first ever job
- Moving from self-employment into employment
- Starting to receive company benefits or a pension mid-year
How it fixes itself
Usually on its own. Once HMRC receives your details, typically after your employer's first submission, it issues a cumulative code and your next payslip includes a correction for the overpayment. Most emergency codes resolve within one or two pay periods without any action.
The bit HMRC does not spell out
You can speed this up considerably by completing the starter checklist your employer offers when you have no P45. People skip it because it looks like optional paperwork. It is the thing that tells HMRC which of the three starter situations you are in, and without it your employer must default to the most cautious code, which is the one that overtaxes you.
If you are still on an emergency code after two pay periods, contact HMRC rather than waiting. Nothing forces the correction to happen automatically after that point.
Common mistakes
- Skipping the starter checklist. It is the fastest route to the right code.
- Waiting for the year end. Two pay periods is long enough before chasing.
- Assuming the money is lost. Overpaid PAYE comes back through the code.
Try it on your own numbers
This is the same calculator as the full tool page, using 2026/27 rates.
Your tax code
From your payslip, P45 or P60. We decode it and show the tax it produces.
NI is the same whatever your tax code - it is shown for a full take-home picture only.
Tax-free allowance
· 2026/27
- Salary
- Tax-free under this code
- Taxable income
- Income Tax
- National Insurance
- Take-home (after tax & NI)(after tax)
Yearly
Monthly
Weekly
Estimate only - not tax advice. Your code can include adjustments HMRC holds that this tool cannot see.
What the parts mean
Numbers
Letters
Emergency / non-cumulative code
Tax this code charges across salaries
How take-home and deductions change with salary under . Your salary is on the curve.
Common UK tax codes
| Code | What it means |
|---|---|
Compare saved codes
| Code | Salary | Tax-free | Tax | Take-home | |
|---|---|---|---|---|---|
Key takeaways
- ✓ Emergency codes are non-cumulative: each period is treated as the first
- ✓ W1, M1 and X after your code are the markers
- ✓ They usually overtax you, and the money comes back when the code goes cumulative
- ✓ Completing the starter checklist is the fastest way to avoid one
Check you have got it
3 quick questions. No score is kept, and you can change your mind.
1. What does the M1 marker on a tax code mean?
2. You start a job in September on an emergency code. Why is the tax high?
3. What is the quickest way to avoid an emergency code without a P45?
Sources
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