A P800 is a form that is issued by HM Revenue and Customs (HMRC) in the United Kingdom to inform an individual of their tax liability for the tax year. The form is issued after the individual has submitted their tax return and after HMRC has calculated their tax liability based on the information provided in the return.

The P800 form provides a breakdown of the individual's income, tax, and National Insurance contributions for the tax year, and it shows whether they have paid the correct amount of tax or whether they have overpaid or underpaid tax. If the individual has overpaid tax, the P800 form will include information about how to claim a tax refund. If the individual has underpaid tax, the form will include information about how to pay the outstanding amount.

It is important to review the P800 form carefully and to ensure that the information it contains is correct. If you spot any errors or discrepancies, you should contact HMRC as soon as possible to have them corrected. If you have any questions about your P800 form or need help with your tax return, you can contact HMRC for assistance.