Explainer

What Is a P800?

Independent UK guidance for the 2026/27 tax year transition. We are not affiliated with HMRC or GOV.UK, and tax calculation letters are usually sent between June and March of the following tax year.

A P800 is an HMRC tax calculation that reviews how much tax you paid against how much tax HMRC believes should have been paid for a tax year. Many UK taxpayers first meet it as a P800 notice or HMRC letter and search it because they want to know whether they are due a refund.

If you are new to the term, the most important point is that the P800 itself is not automatically a payout. It is the explanation of the tax position, and the wording on it decides what your next step should be. If you already know the letter shows an overpayment, you can jump next to the refund guide or the online claim guide.

A P800 is a tax calculation from HMRC.

It can show either an overpayment or an underpayment.

The next step depends on what the calculation says.

How HMRC works out the result

A P800 is effectively a comparison between what HMRC believes should have been taxed and what was actually taken during the year. This is the basic logic behind the tax calculation before any refund or underpayment outcome is shown.

Total income

HMRC records your pay, pension, savings interest and other taxable income for the year.

Minus allowance

Your Personal Allowance and any other relevant reliefs are taken into account.

Taxable income

This is the amount HMRC believes should actually be taxed.

Compared with tax paid

HMRC compares that figure with the tax already taken through PAYE or other routes.

P800 result

The outcome is either a refund due or tax still to be paid.

What information a P800 notice usually includes

A typical P800 explains the tax year, the income HMRC considered, the tax that was paid, and the amount that HMRC believes should have been paid instead.

This is why readers often see the document described as a tax calculation rather than a claim form. It is there to explain the tax position first, not to act as a generic refund letter without context. If you want to see what a typical P800 letter looks like and where to find key details, check the P800 letter guide.

Why you may receive one

A P800 may be issued when your tax code did not reflect your situation quickly enough, when you changed jobs, or when income details were updated after the end of the year.

It can also appear where HMRC has received updated information from employers, pension providers or banks and building societies. For example, higher savings interest can affect the final calculation if HMRC updates its records after the year ends.

A tax code changed part-way through the year.
You had more than one source of pay, pension or taxable income.
HMRC updated its records after the end of the tax year.

P800 compared with P60 and P45

These forms are often confused, but they do different jobs. A P800 comes from HMRC and reviews your tax position after the year, while P45 and P60 forms come from your employer.

Form	Who sends it	When you get it	What it is for
P60	Your employer	By 31 May if you were employed on 5 April	Summarises your pay and tax for the tax year.
P45	Your employer	When you stop working for them	Shows what you earned and paid in tax so far in the tax year.
P800	HMRC	Between June and March of the following tax year	Explains whether you paid too much or too little tax.

Refunds and underpayments are both possible

A lot of readers search for P800 because they hope it means a refund, and often it does. However, a P800 can also show that too little tax was paid. That is why the wording matters more than the document name alone.

If it shows an overpayment, the next step may be to check the online claim guide. If it shows an underpayment, HMRC may explain how it plans to collect the tax or how to review the calculation further.

What to do next

Once you understand whether the calculation shows a refund or extra tax due, you can move on to the right next step. For a refund, that may mean checking the official claim route. For an underpayment, it may mean reviewing how HMRC plans to collect it.

If anything about the document feels unclear, it is usually better to pause and confirm the meaning first rather than move quickly towards any website asking for details.

Where to go next

Read the refund guideMove from the definition to the wider refund process and next steps.See how to claim onlineGo to the practical claim guide if your calculation says you can continue.Check typical timingSee when HMRC usually sends letters and how long repayment routes can take.Verify the official routeCheck the correct GOV.UK path before entering any details from the letter.

Sources

This page is based on current official guidance and should be checked again if HMRC or GOV.UK updates the process.

GOV.UK: If you have not paid the right amount of taxhttps://www.gov.uk/tax-overpayments-and-underpaymentsUsed for why P800 letters are sent and the June to March timing window.GOV.UK: Tax on savings interesthttps://www.gov.uk/apply-tax-free-interest-on-savingsUsed for the savings-interest example that can affect end-of-year tax calculations.GOV.UK: Your P45, P60 and P11D formhttps://www.gov.uk/paye-forms-p45-p60-p11dUsed for the comparison between P45, P60 and P800.

Common questions

Is a P800 a letter from HMRC?

Yes. In simple terms it is an HMRC tax calculation, often sent as a letter or explained through official guidance.

When are P800 letters usually sent?

GOV.UK says tax calculation letters are sent between June and March of the following tax year.

Can a P800 show that I owe tax?

Yes. It can show either too much tax paid or too little tax paid.

What should I look at first on a P800?

Start with the tax year, the amount shown, and whether the calculation says you overpaid or underpaid tax.

Is a P800 the same as a tax rebate?

Not exactly. A tax rebate or refund may result from a P800, but the P800 itself is the calculation explaining the position.

How do I check my P800 reference number?

Check the reference information shown on your P800 letter itself and only use it on the official GOV.UK route. If you are unsure where to look, compare your letter with the P800 letter guide first.

Can I claim if I have not received a P800 letter?

In most cases you should wait for the P800 letter or official HMRC instruction before trying to claim online. The correct route depends on what your own letter says.

Last updated: 9 April 2026