P800 Letter Explained UK 2026: Tax Calculation & Refund Timing

A P800 is HMRC's annual tax-calculation letter. After the end of each tax year (April), HMRC reconciles your PAYE income against the tax actually deducted by your employer and tells you whether you've overpaid (refund) or underpaid (you owe). Most taxpayers don't realise these letters arrive automatically and that responding promptly can mean an early refund into your bank account.

What a P800 is

The P800 is generated automatically by HMRC's system after they reconcile:

• Your gross income from each employer (via FPS data submitted by employers).
• Your tax deductions from each employer.
• Your taxable benefits in kind (from P11D submissions).
• Your other taxable income (state pension, savings interest, etc., as known to HMRC).

If the totals don't match what your tax code should have produced, you get a P800 letter showing:

• Income totals from each source.
• Tax that should have been deducted.
• Tax actually deducted.
• The difference (refund or underpayment).
• The action to take.

When P800 letters arrive

The reconciliation runs from late June to October each year for the prior tax year. Common arrival timing:

• June-July: simple cases (single PAYE employment, no benefits).
• August-September: more complex cases (multiple employments, BIKs).
• October-November: edge cases requiring HMRC review.

If you don't receive one, it usually means:

• Your tax position reconciled exactly (no over- or under-payment).
• You're in Self Assessment (the SA process replaces P800).
• HMRC's reconciliation hasn't run yet for your record (in which case the letter may arrive later).

You can also generate one yourself at any time via the HMRC Personal Tax Account - see the "Tax overview" section.

What it tells you

A P800 is one of three flavours:

1. P800 with refund

The letter explicitly says you're owed money. Two routes to claim:

• Online claim - sign in to your Personal Tax Account, click "Claim refund", enter your bank details. Refund usually lands within 5 working days for amounts under £10,000.
• Wait for cheque - HMRC will automatically post a cheque if you don't claim online within 21 days. Slower (4-6 weeks) but works without a PTA login.

The online route is much faster. Claim the moment the P800 arrives.

2. P800 with underpayment under £3,000

The letter explains you owe HMRC. For amounts under £3,000, HMRC will collect the underpayment automatically through your tax code in the following tax year - your code reduces by an amount that produces the right deduction over 12 months.

Action: none required unless you want to challenge the calculation. The reduced code automatically applies from next April.

If you want to pay it off early to avoid the K-code or reduced-code effect on monthly cashflow, you can pay direct via your Personal Tax Account.

3. P800 with underpayment over £3,000

For amounts over £3,000, HMRC requires a lump-sum payment within 30 days of the letter. They issue a Simple Assessment notification with payment details.

You can request a Time to Pay arrangement if you can't pay in one go - see our HMRC Time to Pay guide.

Common reasons for P800 refunds

If you got a refund letter, here's typically what happened:

• Emergency tax code (W1/M1/X) for part of the year - common after a job change.
• Wrong tax code - BR or 0T applied where 1257L should have been.
• Multiple employments with codes that didn't sync properly.
• Stopped working part-way through the year - unused Personal Allowance.
• Job-related expenses you forgot to claim during the year.
• Marriage Allowance newly claimed and backdated.
• Tax code carried over a stale benefit-in-kind adjustment that no longer applied.

Common reasons for P800 underpayments

If you got an underpayment letter, typically:

• K-code under-applied - your benefits-in-kind weren't fully reflected in your tax code.
• Multiple income sources - two jobs both used the Personal Allowance.
• State Pension started - DWP told HMRC about a benefit that wasn't yet in your code.
• Self-employed income alongside PAYE that wasn't fully reconciled.
• Backdated pay rise that pushed you into a higher band retrospectively.

How to challenge a P800

If the calculation looks wrong:

1. Cross-check the income figures against your final payslip(s) and any P60(s).
2. Check the BIK figures against your P11D.
3. Sign in to your Personal Tax Account and review HMRC's underlying record (the "Tax history" section).
4. If you spot an error, call HMRC on 0300 200 3300 with your NI number and PAYE reference. Describe the discrepancy precisely (e.g. "my P60 shows gross pay of £35,000 but HMRC's record says £37,000").
5. HMRC will investigate and re-issue the P800 if they accept the challenge. You have 4 years from the end of the tax year to challenge.

P800 vs Self Assessment vs Simple Assessment

Three reconciliation paths exist:

• P800: standard reconciliation for PAYE-only taxpayers. Automatic; informational only for refunds; tax-code adjustment for under-£3k underpayments.
• Self Assessment (SA100): if your income includes self-employment, rental, dividends, foreign income, savings interest above the allowance, or you earn over £150k. You file once per year by 31 January.
• Simple Assessment: a hybrid for taxpayers whose situation is more complex than a P800 can handle but who don't quite need full Self Assessment. Usually triggered when underpayment exceeds £3,000 or when state pension income exceeds the Personal Allowance.

The differences matter because the deadlines and consequences vary. If you're unsure which applies to you, check the most recent letter from HMRC or sign in to your PTA.

What to do if you didn't receive one and think you should have

1. Sign in to your HMRC Personal Tax Account.
2. Click "Tax overview" → "View tax record".
3. The system may show your reconciliation status: "in progress", "complete", or "no reconciliation needed".
4. If complete and the result is a refund/underpayment but you didn't get a letter, request a copy via the PTA messaging or call HMRC.

Sometimes letters get lost in the post or are sent to an old address. If you've moved, update your address on the PTA - HMRC needs current details to send P800 letters reliably.

Why we do not recommend a refund firm for P800-driven refunds

Refund firms typically charge 20-35% of any P800 refund. They simply complete the same online claim form you can do yourself in 5 minutes via the PTA.

For a typical £400 emergency-tax refund, that's £80-£140 lost to a process that takes one cup of coffee. The free DIY route is overwhelmingly the right choice.

Disclaimer

PayslipIQ provides automated educational guidance based on the figures you supply. It is not regulated tax advice. P800 calculations rely on data submitted to HMRC by your employer(s), your pension provider(s), and DWP - accuracy depends on those upstream sources. For substantial discrepancies or contested HMRC determinations, contact HMRC on 0300 200 3300 or use a CTA-qualified tax adviser.