What Is a P800 Tax Calculation from HMRC?

If you have received a P800 letter from HMRC, or if you have heard about P800s and want to know what they are, this guide covers everything you need to know. A P800 is HMRC's way of telling you that they have done the maths on your tax for a particular year, and the amount you paid does not match what you should have paid.

What Is a P800?

A P800 (also called a "tax calculation") is a letter or notification from HMRC that reviews the tax you paid during a tax year and compares it to what you should have paid. It is essentially HMRC's reconciliation of your PAYE records.

A P800 will tell you one of two things:

• **You overpaid tax** and are owed a refund
• **You underpaid tax** and owe HMRC money

You will usually receive a P800 if HMRC's records show a discrepancy. Common triggers include starting or leaving a job, having multiple jobs, receiving state benefits alongside employment, or being on the wrong tax code.

When Are P800s Issued?

HMRC typically sends P800 calculations between June and October, after the end of the tax year on 5 April. So for the 2025/26 tax year (ending 5 April 2026), you might receive a P800 from June 2026 onwards.

However, HMRC processes millions of PAYE records, and they do not always catch every discrepancy. Just because you have not received a P800 does not mean your tax was correct. It simply means HMRC has not identified an issue from their records.

What to Do If Your P800 Shows a Refund

If your P800 says you have overpaid, claiming your money back is straightforward:

**Claim online (fastest method):** Log into your Personal Tax Account at gov.uk. If your P800 is available to claim online, you can request the refund directly to your bank account. This typically takes 5 working days.

**Wait for a cheque:** If you do not claim online within 45 days, HMRC will automatically send you a cheque. This can take longer, sometimes several weeks.

**Call HMRC:** If you cannot access your P800 online, call 0300 200 3300 and ask about your tax calculation. They can process the refund over the phone.

What If Your P800 Says You Owe Money?

Do not panic. If the amount is less than 3,000 pounds, HMRC will normally collect it by adjusting your tax code for the following year. This means slightly more tax will be deducted from your pay over the course of 12 months, spreading the cost.

If the amount is more than 3,000 pounds, or if you are no longer employed, HMRC will write to you asking for payment. You can pay online, by phone, or set up a payment plan.

Can You Disagree With a P800?

Yes. If you believe the P800 calculation is wrong, you have 60 days from the date on the letter to contact HMRC and dispute it. Common reasons for disagreement include:

• HMRC used incorrect income figures
• They did not account for all your tax-free allowances
• Employment dates were wrong
• They included income from a job you did not have

Contact HMRC with your P60, payslips, and any other evidence. If you want to check the calculation yourself first, use a tool like AuditMyTax to verify whether the figures HMRC used match your actual documents.

Why You Should Not Rely on Getting a P800

Here is the thing most people do not realise: HMRC does not send a P800 to everyone who has overpaid. Their system works by comparing data from employers (via RTI - Real Time Information submissions) against expected tax. But the system is not perfect.

You might not get a P800 if:

• Your employer submitted incorrect data to HMRC
• The discrepancy was small and fell below HMRC's threshold for action
• HMRC's records are incomplete

This is why it is worth checking your own tax position proactively. Do not assume that no P800 means no overpayment. Tools like AuditMyTax let you verify the numbers yourself using your actual P60 or payslip data.

P800 vs Self Assessment

If you file a Self Assessment tax return, you will not receive a P800. Self Assessment is its own reconciliation process. P800s are only for people who are taxed solely through PAYE and do not submit a tax return.

If you are employed and also have self-employment income, the Self Assessment return covers everything. You would not get a P800 in addition to your Self Assessment calculation.

The 4-Year Claim Window

HMRC can issue P800s for previous years, but the 4-year claim window still applies. If you have overpaid in a year that is more than 4 years ago, that money is likely gone. Currently in 2026, the furthest back you can claim is the 2021/22 tax year. If you have old P800s you never claimed, check whether they are still within the window.

Key Takeaways

A P800 is good news if it shows a refund, and manageable news if it shows you owe money. The important thing is to act on it promptly, claim online for the fastest refund, and do not assume HMRC will always catch errors automatically. If you want certainty about your tax position, check it yourself using your P60 or payslip records. Your money, your responsibility.