P800 tax calculation
UK tax glossary · Last reviewed: April 2026
HMRC sends P800 notices when their records show a mismatch between tax deducted through PAYE and tax actually owed for the year. This commonly happens after emergency codes, job changes, or multiple employments.
Overpayments shown on a P800 can be claimed online through your Personal Tax Account within 45 days — the refund is usually paid within 5 working days. After 45 days, HMRC sends a cheque automatically.
Underpayments are usually collected through your next year's tax code, spreading the debt interest-free. HMRC can also request immediate payment if the amount is significant or you are about to retire.
Worked example
Changed jobs in August 2026. Old job used 1257L, new job applied BR emergency code. Year-end calculation: tax paid = £1,200 too much. HMRC issues P800 showing refund of £1,200. Claim online and receive within 5 working days.
Common questions
Do I always receive a P800 if I overpaid tax?
Not automatically every year. HMRC checks records after the year closes and only sends P800s when it identifies a discrepancy. Not all overpayments trigger a notice — some go unclaimed. Check your tax via your Personal Tax Account proactively.
How do I know if a P800 letter is genuine?
Genuine P800s are sent by post and do not include a phone number to call or a link to a third-party website. HMRC never asks for payment details via text. If in doubt, log in to your Personal Tax Account directly.
Related resources
TaxHelper provides general information based on published HMRC rates and guidance. It is not regulated financial or tax advice. For decisions involving significant sums, complex circumstances, or if you are unsure, speak to a qualified accountant or HMRC directly.