P800 Tax Refund: Overpayment Explained 2026
Last updated: March 2026 · For informational purposes only — not professional advice.
A P800 is a tax calculation letter sent by HMRC when they believe you've paid the wrong amount of income tax through PAYE. If you've overpaid, it tells you how much you're owed and how to claim it back. If you've underpaid, it explains what you owe and how HMRC will collect it. Around 8 million P800 letters are sent every year, so if you've received one, you're far from alone.
What Is a P800?
The P800 — officially called a "Simple Assessment" or "PAYE tax calculation" — is HMRC's way of reconciling what you've actually paid in tax against what you should have paid. They send these after the end of the tax year (which runs from 6 April to 5 April), typically between June and November. The letter arrives by post, though you can also view it in your Personal Tax Account online.
HMRC calculates your P800 using information from your employer (your P14/P60 data), your pension provider, banks and building societies (for savings interest), and any other income sources they know about. If the total tax paid doesn't match what should have been collected, you'll get a P800.
Why You Might Receive a P800
- Wrong tax code: If your employer used the wrong code, you may have paid too much or too little tax throughout the year.
- Starting or leaving a job: When you change jobs, emergency tax codes are sometimes applied, leading to overpayment.
- Multiple income sources: If you have two jobs or a job plus a pension, your tax-free allowance might not have been split correctly.
- Savings interest changes: If your savings interest exceeded the Personal Savings Allowance, or your bank didn't account for it properly.
- State Pension adjustments: The State Pension is taxable. If HMRC didn't adjust your tax code to account for it, you could owe or be owed tax.
How to Use Our Calculator
Before your P800 arrives — or to double-check HMRC's figures — you can use our tax rebate calculator. Select "Overpaid PAYE" as the rebate type, enter your gross income and total tax paid (both shown on your P60 or final payslip), and the calculator will estimate whether you've overpaid.
If you suspect a wrong tax code was the issue, switch to "Wrong Tax Code" mode. Enter both the code your employer used and the code that should have been applied. The calculator shows the difference in tax and your estimated refund.
How to Claim Your P800 Refund
- Check online first: Log into your Personal Tax Account at gov.uk. If HMRC has processed your P800, you'll see the refund amount and can claim online. This is the fastest method — refunds typically arrive within 5 working days.
- Wait for the cheque: If you don't claim online within 45 days of the P800 being issued, HMRC will automatically send a cheque. This can take up to 60 days from the P800 date.
- Call HMRC if needed: If you can't see your P800 online or disagree with the amount, call the Income Tax helpline on 0300 200 3300. Lines are open Monday to Friday, 8am to 6pm.
What If You've Underpaid?
If your P800 shows you owe tax, don't panic. For amounts under £3,000, HMRC usually collects the underpayment by adjusting your tax code for the following year — so you pay a little more each month rather than a lump sum. For larger amounts, or if you're no longer employed, HMRC may ask for direct payment. You can set up a payment plan if needed.
Common Mistakes
- Ignoring the letter: If you're owed money, you need to actively claim online or wait for the cheque. Don't assume it will happen automatically in every case.
- Not checking the figures: HMRC isn't infallible. Cross-check their calculation against your P60 and payslips. If the income or tax figures look wrong, contact them.
- Paying a claims company: Some companies charge a percentage of your P800 refund. You can claim it yourself for free through gov.uk or by calling HMRC.
Frequently Asked Questions
How long after the tax year ends will I get a P800?
HMRC sends P800s between June and November after the tax year ends on 5 April. So for the 2025/26 tax year, expect any P800 between June 2026 and November 2026. If you think you're owed a refund and haven't received one, you can check your Personal Tax Account online.
Can I get a P800 refund if I'm self-employed?
P800s are only for PAYE taxpayers. If you're self-employed, your tax is reconciled through Self Assessment. Any overpayment or underpayment is handled through your tax return. See our self-employed tax guide for more details.
What if I disagree with my P800?
Call HMRC on 0300 200 3300 within 60 days of receiving your P800. Have your National Insurance number, the P800 reference, and your payslips or P60 ready. HMRC can recalculate based on corrected information. You also have the right to a formal review and, ultimately, to appeal to a tax tribunal.
Check our calculator for a quick estimate of what you might be owed. For more on work-related deductions, read our work expenses guide, or see a real-world example in our office worker scenario.
Common P800 Errors and How to Challenge Them
HMRC’s P800 calculations aren’t always correct — errors do happen. Common issues include missing or duplicated income, incorrect tax codes applied across multiple jobs, or outdated information about your circumstances (e.g. not accounting for a change in marital status or pension contributions). If you spot discrepancies, it’s important to act quickly. You can dispute a P800 by contacting HMRC directly. Before doing so, gather supporting documents: your P60, P45, payslips, P11D forms (if applicable), and any evidence of pension or charitable donations. HMRC will review your case and may issue a corrected calculation. Note that you have up to four years from the end of the tax year to appeal a P800 decision, though earlier is better to avoid delays or interest charges if underpayment is confirmed.
What Happens If You Owe Tax (Underpayment)
While many people associate P800s with refunds, HMRC also uses them to recover underpaid tax. If you owe money, HMRC will outline how they plan to collect it — typically by adjusting your tax code for the following year (‘PAYE collection’) or, in rarer cases, asking you to pay directly via self-assessment. If you’re struggling to pay, contact HMRC as soon as possible. They may offer a Time to Pay arrangement, allowing you to spread payments over several months. Importantly, underpayments over £3,000 (and not recovered via your tax code) must be claimed through self-assessment, and interest may apply if payment is delayed beyond 31 January after the tax year. Always double-check HMRC’s underpayment claim — sometimes what looks like a debt is actually a refund in disguise due to timing or coding errors.
P800 vs Self Assessment: Knowing the Difference
It’s easy to confuse a P800 with a full Self Assessment tax return, but they’re fundamentally different. A P800 is a ‘Simple Assessment’ — HMRC prepares it for you, and you typically have no further action unless you disagree. Self Assessment, on the other hand, is a formal process you (or your accountant) must complete annually if you have untaxed income, are self-employed, or earn over certain thresholds. If you receive a P800 but also receive a Self Assessment invitation, don’t ignore either: the P800 covers PAYE income, while Self Assessment covers other sources. Filing both incorrectly can lead to delays or penalties. If you’re unsure which applies to you, use HMRC’s online tool or consult a qualified tax adviser. For most basic PAYE cases, the P800 is the simplest and fastest way to settle your tax affairs.
Common P800 Errors and How to Challenge Them
HMRC’s P800 calculations aren’t always correct — errors do happen. Common issues include missing or duplicated income, incorrect tax codes applied across multiple jobs, or outdated information about your circumstances (e.g. not accounting for a change in marital status or pension contributions). If you spot discrepancies, it’s important to act quickly. You can dispute a P800 by contacting HMRC directly. Before doing so, gather supporting documents: your P60, P45, payslips, P11D forms (if applicable), and any evidence of pension or charitable donations. HMRC will review your case and may issue a corrected calculation. Note that you have up to four years from the end of the tax year to appeal a P800 decision, though earlier is better to avoid delays or interest charges if underpayment is confirmed.
What Happens If You Owe Tax (Underpayment)
While many people associate P800s with refunds, HMRC also uses them to recover underpaid tax. If you owe money, HMRC will outline how they plan to collect it — typically by adjusting your tax code for the following year (‘PAYE collection’) or, in rarer cases, asking you to pay directly via self-assessment. If you’re struggling to pay, contact HMRC as soon as possible. They may offer a Time to Pay arrangement, allowing you to spread payments over several months. Importantly, underpayments over £3,000 (and not recovered via your tax code) must be claimed through self-assessment, and interest may apply if payment is delayed beyond 31 January after the tax year. Always double-check HMRC’s underpayment claim — sometimes what looks like a debt is actually a refund in disguise due to timing or coding errors.
P800 vs Self Assessment: Knowing the Difference
It’s easy to confuse a P800 with a full Self Assessment tax return, but they’re fundamentally different. A P800 is a ‘Simple Assessment’ — HMRC prepares it for you, and you typically have no further action unless you disagree. Self Assessment, on the other hand, is a formal process you (or your accountant) must complete annually if you have untaxed income, are self-employed, or earn over certain thresholds. If you receive a P800 but also receive a Self Assessment invitation, don’t ignore either: the P800 covers PAYE income, while Self Assessment covers other sources. Filing both incorrectly can lead to delays or penalties. If you’re unsure which applies to you, use HMRC’s online tool or consult a qualified tax adviser. For most basic PAYE cases, the P800 is the simplest and fastest way to settle your tax affairs.