HMRC letters • Plain English

Notice to file a Self Assessment tax return

A Notice to File is HMRC's formal request that you complete a Self Assessment return (HMRC form SA316). When you register for Self Assessment you get one, plus your Unique Taxpayer Reference (UTR). From then you must file by the deadline, even if you owe nothing.

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Who gets this

New to Self Assessment, or newly asked to file.

How to recognise it

  • It gives a tax year and a filing deadline.
  • It includes your UTR, a 10-digit number you need to file.
  • It usually follows registering for Self Assessment, or HMRC deciding you need to file.

What to do

  1. Keep the UTR safe and check that the tax year is right.
  2. Gather your records: income, expenses and every CIS statement.
  3. File online by 31 January after the tax year ends. Paper returns are due 31 October.
  4. If you disagree that you need to file, tell HMRC before the deadline. Do not ignore the notice.

By when

Online 31 January after the end of the tax year; paper 31 October. New to Self Assessment? Register by 5 October.

What happens if you ignore it

  • £100 late filing penalty, then daily penalties, then 5% or £300 at 6 and 12 months.
  • HMRC will keep sending reminders until you file or ask to be removed.

Official GOV.UK pages

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.

CalculatorDo I need to worry about the trading allowance?Allowance or actual expenses? Do you still need to file? Compare the £1,000 limit now with the £3,000 limit announced from 6 April 2027.GuideSelf Assessment deadlines guideEvery key date for 2025/26 and 2026/27, and exactly what it costs to file or pay late.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.

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.