Published: June 2026 | Fact-Checked & Audited By: David Vance, CTA FCA (Chartered Tax Advisor & Accountant)
This guide is fully updated for the 2026/27 HMRC tax year. All calculations and tax rules have been audited against official UK legislation.
Each year, millions of taxpayers in the UK end the tax year having paid the wrong amount of Income Tax. This discrepancy usually occurs due to changing jobs, variable bonuses, incorrect tax codes, or multiple income sources. HMRC audits all PAYE records between June and October and issues a P800 tax calculation letter if there is a mismatch. In this guide, we walk you through how to understand your P800 letter, how to claim your refund safely, and what to do if you owe underpaid tax for the 2026/27 tax year.
P800 Tax Calculation Letter Explained
The P800 is not a bill or a fine; it is an official statement showing the total income you received, the tax you paid, and what you *should* have paid based on HMRC’s cumulative records. It will state one of three things:
- You are owed a refund (Overpaid Tax): HMRC has calculated that you paid too much tax. You can claim this online immediately.
- You owe HMRC money (Underpaid Tax): You did not pay enough tax during the year. HMRC will explain how they plan to collect this.
- Your tax is correct: No action is needed.
How to Claim an Overpaid Tax Refund
If your P800 states you are owed a refund, the process is quick and secure. You can claim your refund online via the Government Gateway or the official HMRC App. The funds will be transferred directly to your bank account within 3 to 5 working days. If you do not claim online within 21 days, HMRC will automatically mail a paper cheque (payable order) to your registered address, which takes up to 14 days to arrive.
To check if your current payroll deductions match your tax obligations and estimate whether you are overpaying, use our free Payslip Calculator.
What People Search For: FAQs on P800 & Tax Refunds
1. What is a P800 letter from HMRC?
A P800 is an official tax calculation letter sent by HMRC if you have paid too much or too little tax under PAYE. It is sent automatically after the tax year ends once HMRC reconciles your payroll records.
2. How long does a P800 refund take to process?
If you claim your P800 refund online, the money is paid directly into your bank account within 5 working days. If you request a paper cheque, it takes up to 21 days to arrive by mail.
3. What causes underpaid tax under PAYE?
Underpaid tax is usually caused by having an incorrect tax code, starting a new job without a P45, or receiving taxable benefits (like medical insurance) that were not declared. Multiple part-time jobs can also lead to underpayments if personal allowances are duplicated.
4. How does HMRC collect underpaid tax?
HMRC normally collects underpaid tax by adjusting your tax code for the following tax year, spreading the repayments over 12 months. This is known as “coding out” the debt. If you owe more than £3,000, or do not have enough PAYE income, they may ask you to pay directly.
5. Can I challenge a P800 underpayment calculation?
Yes, if you believe HMRC’s P800 calculations are incorrect, you can challenge them by providing bank statements, payslips, and P60 forms. Call HMRC or log into your Personal Tax Account to verify your employment history.
6. Is a P800 letter sent to everyone?
No, HMRC only sends P800 letters to individuals whose PAYE deductions did not match their actual tax liability. If you paid the exact amount of tax required, you will not receive a letter.
7. How do I know if a P800 text or email is a scam?
HMRC will never send a text or email with a direct link to input your bank details for a refund. Authentic P800 calculations are sent by post or appear in your official Government Gateway account.
8. What is the deadline to claim a tax refund from HMRC?
You have up to 4 years after the end of the relevant tax year to claim a refund from HMRC. For the 2026/27 tax year, the deadline to claim any overpaid tax is 5 April 2031.
9. Does a change in my salary trigger a P800?
A simple pay rise or salary drop will not trigger a P800 if your employer updates your payroll records correctly. However, if you change employers mid-year and your tax code is not adjusted cumulative, it can lead to a reconciliation discrepancy.
10. Can I get a tax refund if I am unemployed?
Yes, if you stop working mid-year and do not claim benefits, you may have unused Personal Allowance. You can claim a refund before the end of the tax year by submitting form P50 to HMRC.