P800 Tax Calculation Letter Explained: Refund, Underpayment and How to Check It

Why did HMRC send you a P800?

PAYE works payslip by payslip. Once the year ends, HMRC adds up the income every employer and pension provider reported and compares the tax due with the tax taken. A P800 means the two did not match¹.

• Your tax code was wrong for part of the year, for example an emergency code after a job change.
• You had two jobs or pensions in the same month and the allowance was used twice.
• You stopped work and did not claim the overpaid tax back.
• HMRC estimated a taxable benefit, such as a company car or medical cover, and the real figure was different.
• Your savings interest went above your Personal Savings Allowance (£1,000 for basic-rate, £500 for higher-rate taxpayers).
• You received Employment and Support Allowance or Jobseeker's Allowance, which are taxable but paid without tax deducted¹.

How do you check a P800 is right?

Lay the P800 next to your P60 (or P45 for a job you left) for the same tax year. The pay and tax figures for each employer should match. Then check the allowances and any deductions the letter lists, such as an estimate of savings interest or a benefit in kind.

• A job listed twice, or a job you left still showing pay after your leaving date.
• Savings interest that belongs to a joint or closed account, or an ISA (ISA interest is tax-free).
• A company car or medical benefit that ended before the year did.
• A missing Marriage Allowance or pension relief you claimed.
• State Pension income that is shown for the wrong number of weeks.

If something is wrong, contact HMRC through your personal tax account or the income tax helpline before paying an underpayment or spending a refund. Keep payslips, your P60 and bank interest statements to hand.

Worked example: a £419 underpayment through your tax code

Priya changed jobs in 2025/26 and for two months both employers gave her a full month's allowance. Her P800 says she underpaid £419. She pays tax through PAYE, owes less than £3,000 and earns well above her allowance, so HMRC collects it through her 2027/28 tax code instead of asking for a payment³.

As a basic-rate taxpayer, £419 of tax equals £2,095 of allowance (£419 ÷ 20%). Her allowance falls from £12,570 to £10,475, so her code becomes 1047L, and she pays about £35 a month extra for 12 months. A higher-rate taxpayer owing £419 would lose £1,047.50 of allowance (£419 ÷ 40%), giving 1152L.

She could instead pay the £419 in one go before the start of that tax year to keep her code at 1257L³.

What to do if your P800 says you are due a refund

• If the letter says you can claim online, sign in to your personal tax account or the HMRC app, check the figures and claim. Payment reaches your bank within 5 working days².
• If the letter says you will get a cheque, you do not need to do anything; it arrives within 14 days of the date on the letter².
• If you ask HMRC for a cheque instead of a bank payment, allow 6 weeks².
• Check the refund covers everything: if you also paid for work expenses or missed Marriage Allowance, claim those for the same year.

Is this P800 genuine?

A real P800 comes by post or appears in your personal tax account and the HMRC app. HMRC does not text or email you a link to claim a refund, and does not ask for bank details by message⁴. If you are unsure, ignore the link and sign in to your personal tax account directly from GOV.UK to see whether a calculation is waiting.