HMRC letters • Plain English

Simple Assessment letter (tax bill by post)

A Simple Assessment is a tax bill HMRC works out for you, without you filing a return. You can get one if you owe tax that cannot be taken automatically through your income, you owe more than £3,000, or you have to pay tax on your State Pension. If you are registered for Self Assessment you will not get one.

By The HandySums teamLast checked:

Who gets this

Employees and pensioners with a tax bill HMRC cannot collect through the tax code.

How to recognise it

  • The letter says Simple Assessment and shows how your tax was worked out.
  • It lists the income, savings interest or benefits HMRC has included.
  • It has a 14-character payment reference starting with X.
  • It sits alongside P800 letters, but it is for tax HMRC cannot collect another way.

What to do

  1. Check the calculation: income, interest and benefits included.
  2. If anything is wrong, contact HMRC within 60 days.
  3. Pay the full amount by the deadline, in one go or in smaller payments. Use the X reference exactly.
  4. If you cannot pay on time, ask HMRC for help before the deadline.

By when

If the letter arrives before 31 October 2026 (for 2025/26), pay by 31 January 2027. If it arrives on or after 31 October 2026, pay within 3 months of the date of the letter. Contact HMRC within 60 days if it is wrong.

What happens if you ignore it

  • HMRC can add interest and penalties for late payment and may chase the debt.
  • If the figures are wrong and you do not respond within 60 days, the assessment stands.

Official GOV.UK pages

The 60-day and 3-month rules are as published on GOV.UK for letters issued from 31 October 2026. Always follow the date printed on your own letter.

Not sure it is genuine?

Do not use any link or phone number printed in a message you are unsure about. Check the list of genuine HMRC letters, then find HMRC’s contact details on GOV.UK yourself. You never need to upload your letter to HandySums, and we would never ask.

CalculatorWhat has changed for me?Tick your situation and get your own list of every tax change and deadline for 2026/27 and 2027/28, with a £ estimate where we can work one out.CalculatorHow much to set aside from earningsHow much to put aside from each invoice, week or month for Income Tax and Class 4 NI, after any CIS.DatesHMRC datesEvery HMRC deadline that matters to the self-employed, with a calendar file.

Sources and review

Last checked: 1 November 2026. What this letter is, the deadlines and the penalties described on this page. Written and checked by the HandySums team against the GOV.UK pages below. HandySums is independent and not an accountancy firm — see how we check our sums.

A guide, not tax advice. Results and explanations are a guide and HMRC has the final say. Always follow the dates and instructions on your own letter, and check with HMRC or a qualified accountant if unsure.