A P800 is a tax calculation letter from HMRC telling you that you paid too much or too little Income Tax in the tax year that ended on 5 April. You only get one if you're employed or get a pension; HMRC sends them between June and March of the following tax year. If it says you're due a refund, you can usually claim it online and get the funds within 5 working days.
A P800 isn't a bill in itself. It's HMRC squaring up the tax taken through PAYE with what you should have paid. Everything below comes from GOV.UK's guide to tax overpayments and underpayments, and it's current as of October 2026.
Why HMRC sends a P800
- You were put on the wrong tax code, for example because HMRC had the wrong information about your income.
- You finished one job, started another and were paid by both in the same month.
- You started receiving a pension at work.
- You received Employment and Support Allowance or Jobseeker's Allowance.
If you're registered for Self Assessment, you won't get a P800. Any overpayment or underpayment is adjusted automatically through your Self Assessment bill instead.
P800 or Simple Assessment letter?
| Letter | When HMRC uses it |
|---|---|
| P800, tax calculation letter | You've overpaid or underpaid through PAYE and it can be sorted through a refund or your tax code |
| Simple Assessment letter | You owe tax that can't be taken automatically from your income, you owe HMRC more than £3,000, or you have to pay tax on your State Pension |
The difference matters because a Simple Assessment comes with a payment deadline, while most P800 underpayments are collected quietly through your pay. If you get a Simple Assessment letter instead, GOV.UK has a separate route for paying that bill, and you'll need to pay by the deadline it gives.
If your P800 says you're due a refund
| How you claim | When the refund arrives |
|---|---|
| Online, by bank transfer or by requesting a cheque online | Within 5 working days if claimed online |
| Asking HMRC to send a cheque | Within 6 weeks |
| The letter says you'll get a cheque automatically | Within 14 days of the date on the letter, with no need to contact HMRC |
To claim online you need the reference number on your P800 and your National Insurance number. You can also claim through your personal tax account or the HMRC app if you have a UK bank account, or by contacting HMRC. If you're owed tax for more than one year, you'll get a single cheque for the whole amount.
If your P800 says you owe tax
HMRC will usually collect it by changing your tax code, which increases the tax taken from your wages, salary or pension, usually in equal instalments over 12 months from the start of the next tax year. That happens automatically if all three of these apply:
- You pay Income Tax through an employer or pension provider.
- You earn enough above your Personal Allowance to cover the underpayment.
- You owe less than £3,000.
If HMRC can't collect it that way, it'll write to you about how to pay. You can also choose to pay what you owe before the start of the next tax year rather than have it spread through your code. If you're unsure what your code means, our guide to the 1257L tax code explains the most common one.
If you think your P800 is wrong
- Check the figures against your own records. Your P60 shows your pay and tax from an employer for the year, and a P45 covers a job you left during it.
- Look at the benefits and pension income HMRC included.
- Contact HMRC and tell them which amounts you think are wrong and what they should be.
- If HMRC agrees, you'll get a new calculation. If it disagrees, it'll contact you to explain why.
What to do when a P800 lands
- Read which way it goes: refund or underpayment. The letter tells you how to get a refund or pay what you owe.
- For a refund, check whether it says you can claim online or that a cheque is coming automatically, and act on that.
- For an underpayment, check whether it'll be collected through your tax code or whether HMRC will write about another way to pay.
- Compare the income and tax figures with your P60, any P45 and your pension statements before you accept them.
- Keep the letter and its reference number. You'll need the reference to claim online, and it's your record if the code changes next April.
No P800 but you think you're owed?
Not getting a letter doesn't mean nothing's owed. If you think you've paid too much and HMRC hasn't sent a tax calculation letter, GOV.UK points you to the route to claim a refund. And if you think you owe tax but haven't heard anything, contact HMRC rather than waiting, because the underpayment won't go away on its own.
The verdict
Read a P800 the day it arrives. If it's a refund, claim online with the reference number and your National Insurance number, and it'll usually land within 5 working days. If it's an underpayment under £3,000, expect it to come through your tax code over the next year, and if any figure looks off, challenge it with HMRC before that code changes.
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Frequently asked questions
What is a P800?
It's a tax calculation letter from HMRC showing you paid too much or too little Income Tax in the previous tax year.
When are P800 letters sent?
HMRC sends them between June and March of the following tax year.
How long does a P800 refund take?
Within 5 working days if you claim online, 6 weeks if you ask for a cheque, or 14 days from the letter date if HMRC sends a cheque automatically.
How do I pay tax owed on a P800?
HMRC usually changes your tax code and collects it in equal instalments over 12 months from the start of the next tax year, if you owe less than £3,000 and earn enough to cover it.
Why didn't I get a P800?
You only get one if you're employed or get a pension. If you're registered for Self Assessment, adjustments go through your Self Assessment bill instead.
What if my P800 is wrong?
Contact HMRC, say which amounts are wrong and what they should be. If HMRC agrees, it'll send a new calculation.
