If you’ve received a Simple Assessment letter from HMRC, don’t panic—but don’t ignore it, either.
It’s part of HMRC’s process for collecting underpaid tax from individuals with relatively straightforward financial affairs. And while it removes the need for a full Self Assessment tax return, it’s still your responsibility to check that everything’s correct—and pay up on time.
Let’s walk you through what it means, what to check, and how to respond if something looks wrong.
What Is a Simple Assessment?
HMRC uses Simple Assessment to collect tax where:
- You’ve underpaid tax, and
- It can’t be collected through PAYE (your usual payroll deductions)
Each year, HMRC performs a PAYE reconciliation, sending out P800 calculations. If there’s tax still owing that can’t be taken through your wages or pension, they may follow up with a Simple Assessment.
You’ll receive it either:
- By post, or
- In your Personal Tax Account online (if you’ve set one up)
The letter will show your:
- Taxable income
- Tax already paid
- Tax still owed
Check the Figures Carefully
HMRC tries to get it right—but they don’t always.
You should compare the figures in your Simple Assessment against:
- Your P60 or P45
- Bank statements (especially for interest income)
- Letters from the Department for Work and Pensions (DWP)
- Pension and investment summaries
If something doesn’t add up—or you don’t understand where a figure comes from—it’s worth seeking advice before paying.
What to Do If You Think It’s Wrong
If you believe the assessment is incorrect, you have 60 days from the date on the letter to tell HMRC.
You can:
- Call HMRC, or
- Write to them explaining which figures you believe are wrong and what they should be instead
If HMRC agrees, they’ll send you a new Simple Assessment. If not, you’ll receive a decision letter explaining why they believe their figures are correct.
Still not happy? You can appeal—but make sure to do so within 30 days of the decision letter’s date.
Important: You still need to pay the tax on time while your appeal is being processed—unless HMRC tells you otherwise.
How and When to Pay
You can pay your Simple Assessment tax by:
- Online payment
- Bank transfer
- Cheque
The payment deadline depends on when you received your Simple Assessment letter:
| Date Letter Received | Payment Deadline |
| Before 31 October 2025 | 31 January 2026 |
| After 31 October 2025 | 3 months from the letter date |
Late payments attract interest, so don’t miss the deadline!
Need Help Understanding or Challenging a Simple Assessment?
Simple Assessments are meant to simplify things—but if the numbers don’t look right, or you’re not sure where to start, we’re here to help.
Get in touch with Jon or the team today for expert support in checking your assessment, understanding your tax position, and dealing with HMRC with confidence.
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Any questions?
If you’d like a meeting or a video call to discuss this, please get in touch with your favourite Liverpool accountant
- You can ring us on 0151 380 8080
- You can email us at gr****@*********************co.uk