The short answer
What to do when HMRC sends a P800 tax calculation letter: claim a refund, pay an underpayment, check the figures and avoid confusing it with Self Assessment.
A P800 tax calculation letter tells an employee or pension recipient that HMRC has calculated the Income Tax for a year and believes they either overpaid or underpaid. The letter should explain whether you can claim a refund, will receive a cheque, or need to pay or have the underpayment collected through your tax code.
The first decision is to identify which route the letter gives you. Do not use the P800 process if you are registered for Self Assessment for that year: HMRC says your bill is normally adjusted through Self Assessment instead, and you will not receive a P800 or Simple Assessment letter for the same calculation.
Read the outcome on the letter
Online refunds can be quicker
Challenge incorrect figures
What is a P800?
HMRC sends a tax calculation letter, also called a P800, after the end of a tax year when its PAYE information indicates that an employee or pension recipient has paid too much or too little Income Tax. Letters are generally issued between June and March of the following tax year.
Common reasons include an incorrect tax code, finishing one job and starting another in the same month, starting an occupational pension or receiving taxable benefits such as Employment and Support Allowance or Jobseeker’s Allowance. The reason on the letter should be checked against your payslips, P60, pension statements and tax-code history.
A P800 is an HMRC calculation based on the information it holds. It is not a substitute for checking an employer’s payroll, a pension provider’s figures or your wider filing obligations.
If the P800 says you are due a refund
The letter will tell you how the refund can be paid. If it says you can claim online, GOV.UK says you can use the online bank-transfer service or request a cheque online. You will need the reference number from the P800 and your National Insurance number.
You may also be able to claim through your Personal Tax Account or the HMRC app if you have a UK bank account. Use only the official GOV.UK or HMRC service. HMRC does not need you to provide bank details through a suspicious text message or an unverified link.
The current GOV.UK guidance states that an online claim is normally paid within 5 working days. If you request a cheque, the guidance says it can take up to 6 weeks. If the letter says HMRC will send a cheque automatically, you do not need to make a separate claim; GOV.UK says the cheque should arrive within 14 days of the date on the letter.
The timescales are service guidance, not a guarantee that a payment will arrive if identity checks, bank details or the calculation need review. Keep the P800 and the claim confirmation until the refund is received.
If the P800 says you owe tax
HMRC will usually try to collect an underpayment by changing your tax code from the start of the following tax year. The current GOV.UK conditions include that you pay Income Tax through an employer or pension provider, earn enough income above your Personal Allowance to cover the amount and owe less than £3,000.
If HMRC cannot collect the underpayment this way, it will write to you with how to pay. You can also choose to pay before the following tax year starts, using the instructions and payment reference given by HMRC.
Do not assume that a £3,000 figure means every underpayment will be coded out. The tax-code collection route depends on HMRC’s conditions, your income and the information available. Read the P800 and any subsequent tax-code notice together.
What if the P800 is wrong?
If the income, pension, tax deducted, benefits or tax-code information on the P800 is wrong, contact HMRC and explain which amount is incorrect and what it should be. Gather the supporting documents before contacting HMRC, such as:
- P60 and relevant P45 forms;
- payslips and tax-code notices;
- pension statements;
- employer or pension-provider corrections; and
- details of any taxable benefits or other PAYE income.
HMRC says it will send a new calculation if it agrees that the original figures were wrong. If it disagrees, it should explain its position. Correcting the source record with the employer or pension provider may be necessary as well as contacting HMRC.
Do not claim a refund and ignore a known payroll error. A refund based on incorrect information can later be reversed, leaving an unexpected underpayment.
P800 versus Self Assessment and Simple Assessment
These routes are not interchangeable:
| Situation | Usual route |
|---|---|
| Employee or pension recipient with a PAYE overpayment or underpayment | P800 tax calculation letter |
| Registered for Self Assessment for the same year | Self Assessment calculation and bill |
| Tax cannot be collected automatically, tax due is over the coding-out limit, or State Pension tax needs collection | Simple Assessment may apply |
| Refund after leaving a job before the end of the tax year | Check the P45/P50 route and the specific circumstances |
Receiving a P800 does not automatically mean you need to register for Self Assessment. Conversely, a P800 does not remove a Self Assessment obligation created by untaxed income, capital gains, foreign income or another filing trigger.
For a return obligation, read the Self Assessment registration guide. For a Simple Assessment letter, use the Simple Assessment guide. For an employment-leaving refund, see the tax refund after leaving a job guide.
A later notice can include bank interest
HMRC's September 2026 Agent Update says it will begin issuing P800 calculations or PA302 Simple Assessment notices from late September for bank and building-society interest earned between April 2025 and April 2026. Some people may receive a second Simple Assessment notice after HMRC obtains interest information that was missing from the first notice.
When a second notice covers the same tax year, HMRC says the total shown can include the amount from the first notice even if it has already been paid. Compare the two notices and deduct payments already made; do not pay the displayed total twice. A customer who is already registered for Self Assessment for that year should follow the relevant Self Assessment route instead.
P800 safety and scam checks
Tax refunds attract phishing attempts. Treat an unexpected text or email as a prompt to verify your position, not as proof that a refund exists. Open GOV.UK or the HMRC app directly, compare the P800 reference and do not disclose passwords, one-time codes or full bank details through an unverified link.
HMRC’s genuine-message guidance can help assess a message, but it does not prove that the tax calculation itself is correct. Verify the refund through the official Personal Tax Account, HMRC app or the contact route on GOV.UK.
A practical P800 checklist
Work through a P800 safely
- 1Confirm the tax year, name, National Insurance number and the income sources shown on the letter.
- 2Identify whether HMRC says you are due a refund, will send a cheque or owe tax.
- 3Compare the calculation with your P60, P45, payslips, pension statements and tax-code notices.
- 4Use the official refund or payment route stated by HMRC, not a link in an unverified message.
- 5Contact HMRC or the employer/pension provider if a figure is wrong and keep the supporting evidence.
- 6Retain the P800, claim confirmation, payment record and any replacement calculation.
Frequently Asked Questions
Evidence and decision checks
A reliable uk p800 tax calculation letter 2026 27 review starts by fixing the tax year and the date on which the relevant event happened. Record the person's or business's status, the income or transaction category, the amount before tax, tax already withheld, and any election or claim being relied on. Do not combine a headline figure with a final liability: the result can change when another income source, a payment date, an ownership interest or a qualifying condition is added.
Keep the source documents behind every important input. Depending on the subject, that may include payslips, invoices, bank statements, contracts, provider statements, travel records, HMRC notices, payroll submissions, valuations or correspondence. Where an amount is apportioned, write down the method and retain the underlying total. If a correction is made, preserve the original figure and explain the reason, date and evidence for the replacement.
Before relying on the result, check the current official guidance for the same tax year and jurisdiction. Distinguish enacted law from a consultation, draft measure, announcement or future proposal, and record the effective date. Reconcile the final estimate to the relevant return, payroll record or HMRC account. A calculator or explanatory guide can support a decision, but it cannot replace the eligibility test or the official filing and payment process.
Evidence and decision checks
A reliable uk p800 tax calculation letter 2026 27 review starts by fixing the tax year and the date on which the relevant event happened. Record the person's or business's status, the income or transaction category, the amount before tax, tax already withheld, and any election or claim being relied on. Do not combine a headline figure with a final liability: the result can change when another income source, a payment date, an ownership interest or a qualifying condition is added.
Keep the source documents behind every important input. Depending on the subject, that may include payslips, invoices, bank statements, contracts, provider statements, travel records, HMRC notices, payroll submissions, valuations or correspondence. Where an amount is apportioned, write down the method and retain the underlying total. If a correction is made, preserve the original figure and explain the reason, date and evidence for the replacement.
Before relying on the result, check the current official guidance for the same tax year and jurisdiction. Distinguish enacted law from a consultation, draft measure, announcement or future proposal, and record the effective date. Reconcile the final estimate to the relevant return, payroll record or HMRC account. A calculator or explanatory guide can support a decision, but it cannot replace the eligibility test or the official filing and payment process.
What should I do if my P800 says I am due a refund?
How long does a P800 refund take?
How does HMRC collect a P800 underpayment?
Can I receive a P800 if I file Self Assessment?
What if the P800 calculation is wrong?
Is a P800 refund text message genuine?
Why did I receive a second Simple Assessment notice for bank interest?
Does bank interest always go on a P800?
Read the official P800 overview, the refund guidance and the underpayment guidance. For a broader PAYE comparison, use the UK Salary Calculator, remembering that a calculator cannot verify the figures in your P800.
Official sources
Related Guides
UK Tax Refund After Leaving a Job 2026/27 — P45 & P50 Guide
How to claim a UK PAYE tax refund after leaving work: when P50 applies, what your P45 shows, what to do if you start another job and when HMRC adjusts your tax code.
P11D UK 2026/27 — Benefits in Kind, Tax Codes and Deadlines
What a UK P11D shows for 2026/27: taxable benefits, P11D(b), Class 1A National Insurance, payrolling, deadlines and how to check errors.
P60 UK 2026/27 — What It Shows and How to Check It
Understand the UK P60 for 2026/27: when employers issue it, what the figures mean, how it differs from P45 and P800, and how to fix errors.
Review notes and assumptions
Reviewed
2026-09-20
Assumptions
- This guide reflects GOV.UK P800 and tax-overpayment guidance checked on 20 September 2026. The instructions and amounts on the individual P800 letter take precedence.
- The reader is an employee or pension recipient who is not filing the same tax year through Self Assessment; Self Assessment bills follow a different process.
- This guide explains the administrative next step and does not recalculate the tax figures in a P800 or determine whether an underlying employer, pension or tax-code record is correct.