Answers · UK 2025/26

What is a P800 tax calculation and what should I do if I get one?

A P800 is a letter HMRC sends after the tax year ends if their records show you have paid too much or too little Income Tax through PAYE. If you have overpaid, it explains how to claim your refund; if you have underpaid, it explains how much you owe and how it will usually be collected through an adjusted tax code.

Last updated: 2 July 2026Last reviewed: 2 July 2026How we verify

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HMRC automatically reconciles PAYE tax records after each tax year ends (5 April), and if the numbers do not match what should have been paid, they issue a P800 tax calculation to explain the discrepancy. **Why mismatches happen** Common causes include changing jobs partway through the year (leading to incorrect tax code application for a period), having more than one job or pension simultaneously, receiving employment benefits that were not fully reflected in your tax code, starting or stopping receiving certain taxable state benefits, or errors in the tax code your employer was given. **If you're owed a refund** The P800 will state the refund amount and explain how to claim it -- often via a simple online claim through your Personal Tax Account on gov.uk, with the money typically paid within about five working days once claimed online, or by cheque within a few weeks if you do not claim online in time. **If you owe HMRC money** Small underpayments (under £3,000) are usually collected automatically by adjusting your tax code for the following tax year, spreading the repayment across your regular pay rather than requiring a lump sum -- for larger amounts, HMRC may ask for a more direct repayment arrangement. **P800 vs Simple Assessment** A P800 is distinct from a Simple Assessment, which HMRC uses in some other situations (such as State Pension income exceeding the Personal Allowance) -- both are automatic HMRC-generated calculations, but they arise from slightly different circumstances and have different response processes. **Checking the calculation is correct** Do not assume the P800 is automatically correct -- check the income and tax figures shown against your own P60, P45 or payslips, since HMRC's calculation depends on the information submitted by employers and other sources, which can occasionally be wrong or incomplete, leading to an incorrect refund or demand. **Timing** P800s are typically issued between June and October/November following the end of the relevant tax year, once HMRC has received and processed the necessary PAYE data from employers -- if you have not received one but believe you have overpaid tax, you can also proactively check and claim via your Personal Tax Account rather than waiting. **Scam warning** HMRC does not ask for bank details by text message or email to process a tax refund -- P800 refund claims are made directly on gov.uk through your verified Personal Tax Account login, and any unsolicited message asking you to click a link and enter card details to "claim your refund" should be treated as a likely scam. **Practical tip** If you receive a P800 showing an underpayment you do not understand or believe is wrong, contact HMRC to query it before the tax code adjustment takes effect -- catching an error early is much simpler than trying to unwind an incorrect tax code change partway through the following year.