You can check if HMRC owes you a tax refund online through your Personal Tax Account or the HMRC app. Both show your tax code, an Income Tax estimate, and let you claim a refund. HMRC also sends a P800 tax calculation letter between June and March if you have overpaid.
Personal Tax Account (gov.uk) - Your Income Tax estimate and tax code, plus the option to claim a...
The HMRC app - Your tax code, an estimate of the tax you need to pay, and the option to claim a...
P800 tax calculation letter - Sent between June and March if you are employed or get a pension;...
Your tax code and payslip - Whether your tax-free Personal Allowance is being applied correctly; a...
Your Self Assessment account - For people who file a return, your bill is adjusted automatically;...

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