HMRC makes mistakes and you have rights when they do. Describe your situation and get instant plain English guidance on challenging tax decisions and getting your money back.
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What you need to know
Your tax code tells your employer how much tax-free income you get in each tax year. The standard tax code for most employees is 1257L, which means you can earn £12,570 before paying income tax. If your tax code is wrong you may pay too much or too little tax. Common reasons for wrong codes include benefits in kind, previous underpayments, or errors in HMRC's records.
If you are self-employed, have income from property, earn above £100,000, or have other untaxed income, you may need to complete a Self Assessment tax return. The deadline is 31 January each year for online returns and 31 October for paper returns. Late filing results in a £100 penalty even if no tax is owed, with further penalties after three, six and twelve months.
You have the right to appeal any HMRC penalty if you have a reasonable excuse. Reasonable excuses include serious illness, bereavement, an HMRC system failure, or genuinely not knowing you needed to file. You must appeal within 30 days of receiving the penalty notice. If HMRC rejects your appeal you can ask for a review or go to the First-tier Tax Tribunal.
If you have overpaid tax through PAYE, HMRC may refund it automatically at the end of the tax year. If not, you can claim a refund through your personal tax account at GOV.UK or by calling HMRC. You can claim back overpaid income tax for up to four previous tax years. Tax refund companies will do this for you but charge a significant percentage — it is straightforward to do yourself.
HMRC can investigate your tax affairs if they believe there may be errors or underpayment. Most investigations are routine checks rather than fraud investigations. You have the right to professional advice during any investigation. HMRC can normally go back four years for innocent errors, six years for careless errors, and 20 years for deliberate non-compliance.
If HMRC handles your case poorly — including delays, errors, or unhelpful service — you can make a formal complaint. If not resolved to your satisfaction, you can escalate to the Adjudicator's Office (free, independent). As a final step, you can contact your MP who can refer the matter to the Parliamentary Ombudsman.
This guidance is for general information only and does not constitute legal advice. Always verify current figures and legislation on GOV.UK or seek professional advice for your specific situation.