If you’ve received a Simple Assessment letter from HMRC, don’t panic — but do act promptly. This system is used by HMRC to collect tax underpayments from people with relatively straightforward financial affairs, without requiring them to file a full Self Assessment tax return.
Here’s everything you need to know about what Simple Assessment is, how to check it’s correct, what to do if it’s not, and how to make payment on time.
What Is a Simple Assessment?
A Simple Assessment is a method used by HMRC to collect unpaid tax where they have all the necessary information to calculate what you owe.
You may receive one if:
- HMRC finds a tax underpayment during its annual PAYE reconciliation process (usually via a P800)
- The tax can’t be collected through adjustments to your PAYE tax code
- You no longer need to complete a Self Assessment return, but still have a tax bill to pay
The Simple Assessment letter will usually arrive by post, although it might be delivered to your personal tax account if you have one set up. The letter will detail:
- Your taxable income
- Tax already paid
- The outstanding amount now due
Step 1: Check the Assessment Carefully
HMRC’s data is only as accurate as the information they’ve received — and mistakes do happen. So the first thing you should do is check the figures for accuracy.
Compare the details in the Simple Assessment with:
- Your P60 or P45 (if applicable)
- Bank statements
- Letters from the Department for Work and Pensions (DWP)
- Any pension or benefit summaries
- Any savings interest or other income received
If something doesn’t look right or you’re unsure where a figure came from, it’s a good idea to seek professional advice from a personal tax accountant.
Step 2: Disagree with the Figures? Act Quickly
If you think the Simple Assessment is incorrect, you must contact HMRC within 60 days of the date shown on the letter. For more serious or ongoing tax issues, our HMRC tax investigation support may also be useful.
You can:
- Write to HMRC, or
- Call them directly
Make sure you:
- Clearly explain which figures you disagree with
- State what you believe the correct figures should be
- Include supporting evidence if you have it
What Happens Next?
- If HMRC agrees, they’ll issue a revised Simple Assessment.
- If they disagree, they’ll send you a decision letter outlining their reasoning.
If you still don’t agree with HMRC’s position, you have the right to appeal — but you must do so within 30 days of receiving the decision letter.
💡 Important: You must still pay your tax on time, even if you’re appealing — unless HMRC tells you otherwise.
Step 3: How and When to Pay
Tax under a Simple Assessment can be paid:
- Online through your HMRC account
- By bank transfer
- By cheque
The deadline for payment depends on when you received the assessment:
| When You Receive the Letter | Payment Deadline |
| Before 31 October 2025 | 31 January 2026 |
| After 31 October 2025 | Within 3 months of the letter’s date |
Failing to pay by the deadline will result in interest being charged, so don’t delay — even if you’re disputing the amount.
Quick Checklist for Handling a Simple Assessment
✅ Check the date on the letter
✅ Compare the figures with your own records
✅ Contact HMRC within 60 days if you spot errors
✅ Appeal within 30 days of a decision letter if needed
✅ Make sure your payment is made on time
✅ Keep copies of all correspondence
Final Thoughts
A Simple Assessment might come as a surprise — but with the right information and prompt action, it’s a manageable process. The key is to check the details, act quickly if anything seems incorrect, and meet the payment deadlines to avoid interest or penalties.
If you’re unsure about the figures, disagree with HMRC’s calculations, or just want peace of mind, Yorkshire Accountancy can help you navigate the process. We’ll check the accuracy of your assessment, deal with HMRC on your behalf, and make sure everything’s handled properly.
Ready to get help? Get a quote from Yorkshire Accountancy
