P800 tax calculation letter explained
A P800 is the letter HMRC sends when the tax you paid through PAYE doesn't match what their records say you owed for a tax year. It either tells you you're due a refund or that you underpaid. Here's how to read it line by line.
What this document usually is
A P800 Tax Calculation is an end-of-year reconciliation for people taxed through PAYE. HMRC adds up your income, allowances and the tax deducted by your employer or pension provider for a single tax year, then compares it with what should have been paid. If you overpaid, the letter explains how the refund reaches you. If you underpaid, it explains how the amount will be collected — usually through your tax code the following year.
Why a P800 arrives
P800s are triggered automatically, most often because something changed part-way through the year:
- You changed jobs, or had two jobs or pensions at once
- You were on an emergency tax code for part of the year
- You started or stopped receiving a taxable benefit such as a company car
- You claimed expenses, professional fees or Marriage Allowance
- You stopped work part-way through the tax year
How to read the calculation
Work down the letter and check each figure against your own paperwork — your P60, final payslip, and any P45s:
- The tax year the calculation covers (e.g. 2024–25)
- Each source of income listed, and the employer or pension name beside it
- Your Personal Allowance for that year
- Tax already deducted, shown per source
- The final line: overpaid (refund) or underpaid (amount owed)
How a P800 refund is paid
If the letter says you're owed money, HMRC either tells you to claim it online through your Personal Tax Account or GOV.UK app, or says a cheque will be posted. Online claims typically arrive in about five working days; cheques usually take a few weeks. HMRC never emails or texts a link to claim a refund — a message that does is a scam.
If the P800 says you underpaid
Small underpayments are normally collected automatically by adjusting your tax code for a later year, so you pay it back gradually out of your wages or pension rather than in one lump. Larger amounts, or cases where there's no PAYE income to adjust, may come with a Simple Assessment demanding direct payment by a stated date.
Things worth a second look
- An email, text or WhatsApp message claiming to be a P800 refund with a link — HMRC only sends P800s by post or through your Personal Tax Account
- Income listed from an employer you never worked for
- A refund far larger than expected — check before spending it, HMRC can reclaim errors
- A P800 for a year you filed Self Assessment for; the two can conflict
- A payment deadline you can't meet — contact HMRC before the date, not after
What you might need to do next
- Compare every figure with your P60, P45s and final payslips for that tax year
- Sign in to your Personal Tax Account at GOV.UK directly (not via a link) to confirm the letter exists
- If it's a refund, claim it online rather than waiting for a cheque
- If you disagree, call HMRC with the letter reference — corrections are common
- Save the letter and diarise any payment or claim date
Common questions
Q. What is a P800 letter?
A. A P800 Tax Calculation is HMRC's end-of-year check on PAYE tax. It shows your income, allowances and tax paid for one tax year, then states whether you overpaid (refund due) or underpaid (amount to collect).
Q. How long does a P800 refund take?
A. If you claim online through your Personal Tax Account or the HMRC app, the money usually reaches your bank in around five working days. If HMRC posts a cheque instead, it typically takes a few weeks from the date on the letter.
Q. Do I have to do anything if my P800 says I underpaid?
A. Often not — HMRC usually collects smaller underpayments by adjusting your tax code for a future year. Read the letter: if it asks for direct payment by a specific date, that date matters and interest can be added after it.
Q. What if the P800 figures are wrong?
A. Contact HMRC and explain which figure you think is wrong, quoting the reference on the letter. P800s are generated from employer submissions, so a missing P45 or a duplicated employment record can produce an incorrect calculation.
Q. Is my P800 refund email genuine?
A. HMRC does not email, text or message you a link to claim a P800 refund. Refund messages arriving that way are scams. Check by logging in to GOV.UK yourself.
Q. Can ClariDoc explain my P800?
A. Yes. Upload the letter and ClariDoc summarises what the calculation says, whether you're owed money or owe it, any deadline, and a next-step checklist in plain English. ClariDoc doesn't give tax advice.
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Important disclaimer
This guide is general information about how HMRC P800 letters work. It is not tax advice and does not replace guidance from HMRC or a qualified tax professional. For personal advice, contact HMRC or an accountant.
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