Understand your payslip and check your tax code

Help me understand my payslip and check my tax code.

My payslip lines: [paste them, without my name, National Insurance number or employee ID]
My tax code: [e.g. 1257L, BR, W1 or M1]
What changed: [e.g. pay is lower than last month]
What I expected: [and why]

Ask me up to 3 short questions first if anything important is missing. Wait for my answers.

Then:
1. Each line in plain English: what it is and why it's there.
2. What my tax code letters and numbers usually mean, marked "check on GOV.UK".
3. Possible reasons for the difference, from most to least likely, without saying which one it is.
4. Polite questions to ask payroll.
5. How to check my tax code with HMRC on GOV.UK.

Not tax advice. Only use what I've told you, leave blanks for anything I haven't given, and don't invent facts, dates or results. Not tax advice. UK English.

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