If you are on the wrong code, the tax office will often put you on an emergency tax code until you contact them about changing it.
You can check your tax code on your online personal tax account, via payslips, or on the HMRC app.
If your tax code begins with 'W1', 'M1' or 'X' you've been placed on an emergency tax code and may need to update your details.
At the end of each tax year, HMRC usually sends a letter out to tell people if they have overpaid or underpaid tax - these are known as P800 letters.
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