HMRC Letter Decoder

What the HMRC Letter Decoder is and why it helps

A brown envelope from HMRC lands on the mat and your stomach drops. You are not alone in that feeling. The HMRC letter decoder exists to take the fear out of that moment by helping you work out, calmly and quickly, what the letter actually is, whether it means money coming to you, a bill you owe, or simply information you need to keep. Most HMRC letters fall into one of a handful of recognisable types, and once you can name the letter you can decide what to do next without panic.

This tool reads your letter using OCR (optical character recognition), which is just a clever way of saying it scans the text from a photo or upload and matches the reference codes and wording against the common HMRC letter types. It is a plain-English guide, not formal tax advice, and it will never ask you to share your bank details. Think of it as a knowledgeable friend who has seen thousands of these letters and can say, in seconds, "this is a P800, it is a refund, here is what it means".

Who gets HMRC letters and why

Almost everyone in the UK receives post from HMRC at some point. You might be an employee on PAYE who never files a tax return, a self-employed sole trader, a landlord, a pensioner, a company director, or someone who simply changed jobs and ended up on the wrong tax code. HMRC writes to people for dozens of reasons: to correct your tax, to ask you to file a return, to confirm your tax code, to remind you about a payment, or to issue a penalty. The letter type and its reference code tell you which conversation HMRC is trying to have with you.

If your income is straightforward and taxed at source through PAYE, you will mostly see tax code notices and the occasional P800. If you complete Self Assessment, you are more likely to see notices to file, statements and, if a deadline slips, penalty notices. Knowing which group you fall into makes the post far less intimidating.

The common HMRC letters, decoded

Here is what each of the main letters means in practice, drawn from what HMRC actually sends and what I see clients receive most often.

P800 tax calculation (refund or underpayment)

A P800 is a tax calculation, usually sent after the tax year ends because HMRC's annual reconciliation found that you paid too much or too little tax through PAYE. If it shows a refund, you can often claim it online and have it paid within days, or HMRC will send a cheque if you do nothing. If it shows you underpaid, do not panic: HMRC normally collects small underpayments by adjusting your tax code over the following year rather than demanding a lump sum. Always check the figures against your own records first. The official guidance on tax overpayments and underpayments explains the process clearly, and our check if HMRC owes you money tool can help you sense-check a refund.

Simple Assessment (PA302), which is a bill

A Simple Assessment, often carrying the reference PA302, is HMRC telling you it has already calculated tax you owe, typically because you have income that cannot be collected through your tax code, such as the State Pension exceeding your Personal Allowance, or some savings interest. You do not need to file a return for it, but you do need to pay. The deadline is usually 31 January after the end of the tax year, or three months from the date of the letter if that is later. If you think the figure is wrong, you have 60 days to query it. Read the Simple Assessment guidance before you pay so you understand your options.

Penalty notices (SA326) and how to appeal

An SA326 is a late-filing penalty notice for Self Assessment. The first penalty for filing late is a fixed £100, even if you owe no tax. After that, daily penalties and percentage-based charges can build up, which is why deadlines matter. The good news is that you can appeal if you have a reasonable excuse, such as a serious illness, a bereavement, or a genuine technical failure. Our self assessment penalty calculator shows how the charges escalate, and the tax deadline tracker helps you avoid them in the first place.

Tax code notices (P2)

A P2 is a PAYE Coding Notice. It tells you the tax code your employer or pension provider will use and how HMRC worked it out: your Personal Allowance, any deductions for benefits like a company car, and any adjustments for underpaid tax. A wrong tax code is one of the most common reasons people overpay or underpay, so it is worth reading. The government's page on tax codes is the definitive reference, and you can check yours with our tax code calculator or read the full tax codes explained guide.

Notice to file (SA316)

An SA316 is a notice to complete a Self Assessment tax return. Once HMRC issues it, you are legally required to file, even if your circumstances changed and you no longer think you need to. If you genuinely do not need to be in Self Assessment, contact HMRC to be taken out, otherwise the obligation, and the penalty risk, remains. Unsure whether you even need to file? Try our do I need to file a tax return checker.

UTR and welcome letters (SA250)

An SA250 is the welcome letter you get when you register for Self Assessment, and it contains your Unique Taxpayer Reference (UTR), a ten-digit number you will use every time you file or pay. Keep it safe. It is information, not a bill, but losing it causes real headaches later.

Statements and payment reminders

Statements summarise what you owe and what you have paid, while payment reminders nudge you before or after a deadline. They are informational, but ignoring them is how a small balance turns into interest and penalties.

How the HMRC letter decoder works with real 2026/27 figures

The decoder matches your letter's reference and wording to a type, then explains the action. To do that accurately it uses the current allowances and rates. Here are the key 2026/27 figures the common letters revolve around.

Figures are for the 2026/27 tax year and the Scottish bands differ, so if you are in the rest of the UK see the UK income tax rates and bands guide.

Two worked examples

Example one: Priya gets a P800 refund

Priya changed jobs in October 2026 and was put on an emergency tax code for two months, so she overpaid tax. After the tax year ends, HMRC's reconciliation produces a P800 showing she paid £340 too much. Her letter says she can claim online. She logs into her personal tax account, confirms her bank details, and the £340 arrives within five working days. She did not need an agent and she paid no fee. If she had ignored the letter, HMRC would eventually have sent a cheque anyway. To understand how emergency codes cause this, see our emergency tax calculator.

Example two: Geoff gets a Simple Assessment (PA302)

Geoff is 68 and retired. His State Pension is £11,900 and he has a small private pension of £4,000, plus £900 of savings interest. His total income tips just over his £12,570 Personal Allowance, and the tax on the excess cannot be collected through a code because the State Pension is paid without tax taken off. HMRC sends a PA302 for £286. Geoff checks it against his pension statements, agrees it is right, and pays online before the deadline. Because his savings interest is under his £1,000 Personal Savings Allowance, none of that is taxed. Pensioners in this position can sanity-check the numbers with our personal savings allowance calculator.

Common mistakes people make

• Ignoring the letter. A penalty notice does not go away if you bin it. Even a refund letter is worth acting on so the money reaches you sooner.
• Assuming every letter is a bill. Many are refunds or pure information. Decode it before you worry.
• Paying without checking. HMRC makes mistakes too. Always reconcile a PA302 or P800 against your own records before paying or claiming.
• Missing the 60-day window. Simple Assessment and many penalties have time limits to query or appeal. Diarise the date.
• Falling for refund-claim companies. Never pay an agent a fee, or hand over a percentage, to claim a refund that is already yours. If a P800 says you are owed money, you can claim it directly from HMRC for free in minutes. Be especially wary of texts, emails or callers promising a "tax rebate" and asking for your bank or card details, as these are almost always scams.

How to use this tool, step by step

Using the HMRC letter decoder is simple. Take a clear photo of your letter or upload a scan, and the OCR reads the reference code and key phrases. The decoder then tells you the likely letter type, whether it means a refund, a bill or information, and the sensible next step. From there you can jump to the right calculator to check the figures, for example the income tax calculator for a P800, or the self assessment tax calculator if you have a notice to file. Remember the decoder is a guide to help you understand the post, not a substitute for HMRC's own figures or professional advice.

Clear next steps

Once you know what you are holding, the path is usually short. For a refund (P800), claim it online or wait for the cheque. For a bill (PA302 or a Simple Assessment), check it, then pay by the deadline. For a penalty (SA326), see whether you have a reasonable excuse and appeal in time, and file the outstanding return immediately to stop charges growing. For a notice to file (SA316), either file or ask to be removed from Self Assessment. For a tax code notice (P2), check the code is right and contact HMRC if it is not. And keep your UTR letter (SA250) somewhere safe.

If your situation is more involved, perhaps you are a landlord facing Section 24 changes or a director weighing salary versus dividends, it is worth speaking to an accountant, or checking the Self Assessment deadlines guide first. These figures are for the 2026/27 tax year and your own circumstances may differ, so always confirm with HMRC or a qualified adviser before acting on anything important.

Who should use this calculator

HMRC correspondence uses reference codes that mean little to most people, and the tone rarely distinguishes routine from urgent. This decodes what a letter is, what it wants, and by when — so a P800 tax calculation is not confused with a demand, and a genuine deadline is not missed.

It also helps with the security question. HMRC-branded scam letters, texts and emails are common, and a real letter has characteristics you can check. HMRC will never ask for card details by text or email, and never threatens immediate arrest — if in doubt, contact them using a number from GOV.UK, never one printed in the message.

What this calculator assumes

• Guidance is based on the reference or letter type you provide.
• Common types include P800 tax calculations, SA250 registration notices, penalty notices and code change notifications.
• Deadlines quoted are the standard ones for that letter type.
• The output is general guidance, not advice on your specific case.

Limitations — what it does not cover

• Your actual HMRC record, which only they and your online account hold.
• Whether the letter is genuine. Verify anything unexpected through GOV.UK or your Personal Tax Account rather than the contact details in the letter.
• Appeal rights and deadlines, typically 30 days for a penalty, and what counts as a reasonable excuse.
• Time to Pay arrangements, available if you cannot pay in full — contacting HMRC early is materially better than waiting.
• Compliance checks and investigations, where professional representation is usually worth it.
• Interest and penalties accruing while a dispute is unresolved.