HMRC Simple Assessment Letters: Verify and Respond Guide

If you’ve received a letter marked “Simple Assessment” from HMRC, the first thing to do is breathe — and then verify. Scammers increasingly mimic this specific letter format, and the stakes for getting it wrong in either direction are real. This guide walks you through exactly what genuine Simple Assessment letters contain, how to check if yours is authentic, and what steps to take whether you owe tax or suspect a scam.

Delivery methods: post or personal tax account ·
Owe threshold: £3,000 or more ·
Multiple letters possible: for 2024-25 tax year ·
Issued from: June 2025 onwards ·
Official source: GOV.UK

Key details from HMRC Simple Assessment correspondence are summarised in the table below.

Why did I get an HMRC simple assessment?

HMRC sends Simple Assessment letters when it has enough information to calculate tax you owe, but that tax cannot be automatically collected through your PAYE code. This typically happens when you have untaxed income — savings interest being the most common example.

Owe Income Tax not deducted at source

If your total untaxed income creates a tax liability of £3,000 or more, HMRC issues a Simple Assessment rather than adjusting your tax code. The letter details exactly how much tax is owed and why, based on data HMRC already holds about your circumstances.

Owe £3,000 or more

The £3,000 threshold is the key trigger. HMRC calculates the tax on your untaxed income and sends the bill directly, rather than waiting for you to declare it through Self Assessment. Brown Butler, an accountancy firm, notes that legitimate Simple Assessment letters include detailed calculations and never request sensitive information via email or text.

What is the purpose of a simple assessment?

A Simple Assessment is HMRC doing the math for you, using information it already has. Instead of requiring you to file a Self Assessment return, HMRC performs the calculation and sends you the result.

Calculate tax owed

HMRC draws on data from banks, building societies, and other payers to calculate interest and other untaxed income you received. The letter explains which data sources HMRC used, so you can check for errors. GOV.UK maintains a list of all genuine HMRC letter types, including Simple Assessment (code IDMS99P), last updated 16 April 2026.

Simplify tax payment

The assessment gives you a clear amount due with payment options and a deadline. The official HMRC guidance instructs taxpayers unable to pay in full to call 0300 322 7835 to discuss a payment plan. GOV.UK lists the payment overview at www.gov.uk/simple-assessment.

Who has to pay a simple assessment?

Not everyone receives Simple Assessment letters, and receiving one doesn’t mean you’ve done anything wrong. The criteria are purely about income type and amount.

Taxpayers owing specific amounts

If you owe £3,000 or more in Income Tax that wasn’t collected via PAYE, you fall into the Simple Assessment category. GOV.UK confirms that Simple Assessment covers savings interest, redundancy or termination payments above certain thresholds, and other income where tax was not already deducted.

Those with untaxed income

The core common thread is untaxed income. This includes savings interest above the Personal Savings Allowance, PAYE settlement agreements, and certain state benefits. Multiple Simple Assessment letters may arrive for the 2024-25 tax year if you have several types of untaxed income — accountancy firm ATT advises checking each letter separately.

How to spot fake HMRC letters?

Scammers have become adept at mimicking HMRC letter formats, but several telltale signs distinguish genuine communications from fraud.

Check official formatting

Legitimate HMRC letters include a reference number, specific tax calculation details, and official HMRC contact information. Howard’s Accountants points to a common fake letter red flag: wrong UTR (Unique Taxpayer Reference) digit count. A genuine UTR has 10 digits — if a letter shows 6 digits, it’s fake.

Verify via GOV.UK

The most reliable verification step is checking GOV.UK’s official list of HMRC communications. GOV.UK publishes every genuine letter, email, text, and QR code type — updated regularly. Compare your letter against this list. Taxd adds that fake letters often include urgent language, threats, poor grammar, and spelling errors.

How do I contact HMRC about Simple Assessment?

If your Simple Assessment letter is genuine and you have questions or cannot pay in full, HMRC provides clear contact channels.

Online via personal tax account

Log into your personal tax account at GOV.UK to view the full Simple Assessment details, check the calculation, and make payments. GOV.UK lists the check page at www.gov.uk/check-simple-assessment. If you disagree with the assessment, you can log a dispute through the same account.

Phone number options

The official Simple Assessment letter instructs calling 0300 322 7835 if you’re unable to pay in full. GOV.UK confirms this number handles payment plan discussions. For scam reports, forward suspicious text messages to 60599 and email phishing@hmrc.gov.uk.

Steps to verify and respond to your letter

A systematic approach protects you whether the letter is genuine or a scam.

1. Check the letter code: Genuine Simple Assessment letters use code IDMS99P. Look for this in the letter header.
2. Verify the UTR: Your Unique Taxpayer Reference should have 10 digits. Shorter sequences indicate a fake.
3. Cross-reference on GOV.UK: Visit GOV.UK’s letter verification page and compare your letter against the official list.
4. Check via personal tax account: Log in at www.gov.uk/check-simple-assessment to see whether HMRC has recorded the same assessment.
5. Note the deadline: Genuine Simple Assessment letters give 28 days to respond. Mark this date.
6. Contact HMRC if needed: Call 0300 322 7835 for payment help, or use the dispute function in your personal tax account.
7. Report scams: Forward suspicious texts to 60599 and email phishing@hmrc.gov.uk to report fraudulent letters.

What the experts say

“If you receive further requests for information to be sent to an email address that does not end in ‘hmrc.gov.uk’, they will not be genuine and you should report this to HMRC.”

— HMRC (GOV.UK official guidance)

“Phishing campaigns linked to HMRC follow a clear calendar pattern. Activity ramps up between December and April.”

— Zenzero (Cybersecurity analysis)

The implication is clear: scam activity rises precisely when legitimate HMRC communications increase around Self Assessment deadlines. This timing advantage lets fraudsters blend in with genuine mail. Which.co.uk reports that scammers now mimic not just letters but also emails with HMRC employee signatures and texts with official-looking links.

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Recipients of HMRC Simple Assessment letters often encounter similar P800 P800 savings tax letters regarding unexpected savings tax bills exceeding the £3,000 threshold.

Frequently asked questions

For UK taxpayers, the takeaway is straightforward: verify before you act. A genuine Simple Assessment is manageable — HMRC offers payment plans, and the calculation is transparent. A fake letter, if acted upon, can drain your accounts or hand criminals your identity. Two minutes checking GOV.UK is the cheapest insurance you’ll find.