What is a P800? Your Ultimate Guide to HMRC's Overpayments and Underpayments Tax Letter
Received a P800 tax calculation from HMRC? Our UK guide explains what it means if you've overpaid or underpaid tax, how to claim a refund, and how to respond.
Receiving an official-looking brown envelope from HM Revenue & Customs (HMRC) can cause a moment of concern. If that letter is a P800 tax calculation, it means HMRC has reviewed your tax records and believes you've either paid too much or too little tax. While this might sound alarming, a P800 is often the first step to getting a tax refund you're owed or a clear explanation of tax you need to pay.
At Plouta, we're dedicated to demystifying financial jargon and empowering you with the knowledge to manage your money with confidence. This guide will explain exactly what a P800 is, why you might receive one, how to understand it, and what action you need to take – whether you're due a refund or owe more tax.
What you will learn in this guide: ⤵
What a P800 Is: A clear definition and its purpose.
Who Receives a P800: Understanding who is likely to get one (and who isn't).
Common Reasons for a P800: Why your tax calculation might have been incorrect.
Reading Your P800: How to understand the breakdown of your income and tax.
You're Due a Refund: The step-by-step process for claiming your money.
You Owe Tax: How HMRC typically collects underpayments.
What to Do if It's Wrong: How to check and challenge a P800.
Protecting Yourself: How to spot P800-related scams.
What is a P800 Tax Calculation Letter?
A P800 is an official tax calculation sent by HMRC after the end of a tax year (which runs from 6th April to 5th April). It is sent to individuals who pay tax through the PAYE (Pay As You Earn) system – primarily employees and those receiving company or private pensions.
Its purpose is to show HMRC's calculation of:
Your total taxable income for the tax year.
The tax allowances you were entitled to.
The amount of tax you should have paid.
The amount of tax you actually paid.
The P800 then states the final result: whether you have paid too much tax and are due a refund, or paid too little tax and have an underpayment.
Who Receives a P800 (and Who Doesn't)?
You are only likely to receive a P800 if you pay tax through PAYE. HMRC sends them out between June and November following the end of the tax year.
You will not usually receive a P800 if you are registered for Self Assessment. This is because any over or underpayment of tax for PAYE income is automatically calculated and reconciled when you complete your Self Assessment tax return.
Common Reasons for Receiving a P800
A discrepancy in your tax can happen for many simple reasons as the PAYE system tries to estimate your tax liability in real-time. You might receive a P800 if:
You started a new job and were on an emergency tax code for a period.
You had more than one job or pension at the same time.
You received taxable company benefits that weren't correctly accounted for in your tax code (e.g., a company car or private medical insurance).
Your income changed significantly during the year.
Your tax-free Personal Allowance was incorrect (e.g., due to your income exceeding £100,000, or a change in your eligibility for Marriage Allowance).
You started receiving your State Pension, which is taxable but paid without tax being deducted.
How to Respond to Your P800 Letter
Your P800 will clearly state whether you have overpaid or underpaid tax. Your next steps depend on this outcome. Crucially, before you do anything, you should check the figures on the P800 against your own records (like your P60 or P45) to ensure they are correct.
Scenario 1: Your P800 Says You're Due a Refund
This is great news! The letter will explain how to get your money back.
Claiming Online: In most cases, the letter will direct you to claim your refund online via the GOV.UK service. This is the fastest method. You will need your National Insurance number and details from the P800. You can have the money paid directly into your UK bank account.
Automatic Cheque: If you don't claim your refund online within a set period (e.g., 21 days), HMRC will usually post you a cheque automatically. However, this is a slower process.
Timescale: Once you claim online, the money usually arrives in your bank account within 5-10 working days. A cheque can take several weeks to arrive.
Scenario 2: Your P800 Says You Owe Tax
This means you have an underpayment. Don't panic; the P800 is not a formal demand for immediate payment. HMRC has a standard process for collecting what is owed.
If you owe less than £3,000: HMRC will almost always collect the underpayment automatically through your tax code. They will adjust your code for the next tax year, meaning you'll pay slightly more tax each month to gradually pay off the amount owed. This avoids the need for a lump sum payment.
If you owe £3,000 or more (or it can't be collected via your code): HMRC will contact you separately to arrange payment. You can usually pay online, or if you are concerned about affordability, you can contact HMRC to discuss a payment plan ("Time to Pay" arrangement).
What to Do If You Think Your P800 is Wrong
A P800 is only as accurate as the information HMRC holds. If you think the figures are wrong (e.g., an income source is missing or incorrect), you must contact HMRC.
Gather Your Evidence: Collect your P60s, P45s, and any other documents relating to your income for that tax year.
Contact HMRC: Call their Income Tax general enquiries helpline. The contact details will be on the P800 letter.
Explain the Discrepancy: Tell the adviser which figures you believe are wrong and provide the correct ones.
If HMRC agrees, they will issue a revised, correct P800. If you have already received an incorrect refund, you will need to pay it back.
Important: How to Spot P800 Tax Refund Scams
Scammers frequently use the promise of a tax refund to trick people into giving away personal and financial information. Be extremely vigilant.
HMRC will never email, text, or WhatsApp you about a tax rebate with a clickable link.
Official P800 notifications come via post or through your secure Personal Tax Account on GOV.UK.
Be wary of any communication with poor grammar, spelling mistakes, or that creates a false sense of urgency.
Never provide personal or bank details in response to an unsolicited email or text message.
What to Do: Report suspicious emails by forwarding them to phishing@hmrc.gov.uk and texts by forwarding them to 60599.
Quick Takeaway Points:
What it is: A P800 is an end-of-year tax calculation for those in the PAYE system.
Why you get one: Because HMRC's records show you've paid either too much or too little tax.
Check it Carefully: Always check the figures against your own records (P60s etc.).
Claiming a Refund: If you're owed money, the quickest way is usually to claim online via GOV.UK as instructed in your letter.
Paying an Underpayment: This is usually done automatically through your tax code for the following year if the amount is under £3,000.
Beware of Scams: HMRC will not text or email you with a direct link to claim a refund.
Conclusion: Your P800 – A Tool for Financial Clarity
Receiving a P800 tax calculation letter is a normal part of the UK tax system. It’s an opportunity to ensure your tax affairs are in order and to get back any money you've overpaid. By understanding what the letter means and checking it carefully, you can respond with confidence and maintain control over your finances.
Regularly checking your tax position, either through documents like the P800 or via your online Personal Tax Account, is a proactive step towards financial wellness and ensuring you only pay the tax you legally owe.
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Disclaimer: This article provides general information about HMRC P800 tax calculations and is for informational and educational purposes only. It is based on general processes and information available as of June 2025. Tax laws, HMRC procedures, and specific allowance figures can change. This information does not constitute tax or financial advice. Always refer to the official GOV.UK website or consult with a qualified accountant or tax advisor if you are unsure about your specific tax situation.