What is X Tax Code? UK Definition 2026/27
Quick Answer
Emergency tax code suffix indicating HMRC awaiting P45 or starter information.
Definition of X Tax Code
An X suffix on a tax code (like 1257X) indicates an emergency tax code has been applied, usually because your employer hasnt received your P45 from your previous job or your completed starter checklist. HMRC uses cumulative basis initially but may switch to Week 1/Month 1 if information isnt received. Once sorted, your code normalises.
X Tax Code — Key Facts for 2026/27
| Meaning | Emergency code in use |
| Common code | 1257X |
| Triggers | Missing P45, no starter info |
| Resolution | P45 receipt or HMRC info |
How X Tax Code Works — Example
- 1Start new job: 1 March
- 2No P45 from previous employer yet
- 3Starter checklist: Not completed
- 4Employer uses: 1257X code
- 5P45 arrives: Code updated to 1257L
How X Tax Code Affects Your Tax
Emergency codes may result in too much or too little tax being deducted. Usually too much, as you miss personal allowance benefit. The situation normally resolves within a few weeks when HMRC receives correct information.
Official HMRC Guidance on X Tax Code
For official guidance, refer to HMRC's documentation. Tax rules can change, so always verify current rates and thresholds on gov.uk.
HMRC: Tax codesFrequently Asked Questions about X Tax Code
Related Tax Terms
Accuracy Note
This information is for guidance only and is based on 2026/27 tax year rates. Tax rules are complex and your circumstances may differ. For personal advice, consult a qualified accountant or tax adviser.