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Tax Code Decoder Card
Decode any UK tax code in seconds: what 1257L, BR, D0, K, M and N mean, how emergency codes (W1, M1, X) work, and the common reasons your code might be wrong.
What’s Included
- Every common code letter explained in plain English, from L to K.
- Emergency codes (W1, M1 and X) and how to get them fixed.
- Five symptoms that show your code might be wrong, with the likely cause of each.
- A quick action checklist for correcting a wrong code.
Why This Matters for 2026/27
- Your tax code decides how much tax comes off every payslip, and an error can cost you hundreds of pounds a year.
- Emergency codes are common when you start a job without a P45, and they are meant to be temporary.
- S and C prefixes change the rates that apply, so a Scottish or Welsh taxpayer without the prefix may be taxed incorrectly.
Frequently Asked Questions
It is the standard tax code for 2026/27. The number 1257 means a tax-free Personal Allowance of £12,570, and the letter L means the standard allowance.
BR means all your income from that source is taxed at 20% with no allowance. It is common on a second job or pension, or when HMRC has not given the job your allowance.
It is a temporary code, usually ending W1, M1 or X, used when HMRC does not have your details. Tax is worked out on each pay period alone, so it can be wrong until HMRC sends the correct code.
Not directly. HMRC sets your code from the information it holds, so tell HMRC about changes such as a new job, a second job or a benefit and it will update the code.