HMRC letters • Plain English

"You may need to complete a tax return" letter

HMRC sometimes writes to people when its records suggest they should be in Self Assessment, for example untaxed income or a high income child benefit charge. It is a prompt to check, not a bill. You may be told to use the online checker and register if you need to.

By The HandySums teamLast checked:

Who gets this

Anyone with side income, rental income or high savings, even if never in Self Assessment.

How to recognise it

  • It asks you to check whether you need to send a tax return.
  • It points to GOV.UK, not to a link you must click in a message.
  • It does not ask for bank details or promise a refund.

What to do

  1. Use the GOV.UK checker. It does not send your details to HMRC.
  2. If you need to file and are new, register for Self Assessment by 5 October after the tax year ends, then file by 31 January.
  3. If you do not need to file, tell HMRC using the online service. If you do not, HMRC keeps sending reminders.
  4. If you are a sole trader with trading income under £1,000 (before costs), you may not need to register. See the trading allowance guide.

By when

Register by 5 October after the end of the tax year, then file online by 31 January.

What happens if you ignore it

  • If you do need to file and do not, you could be fined and may get a failure-to-notify penalty if tax is unpaid after 31 January.
  • HMRC keeps sending reminders if it thinks you should file.

Official GOV.UK pages

GOV.UK does not publish a single page about these nudge letters, so this page is built from the checker, registration and "no longer need to file" 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.

CalculatorTrading allowance £3,000 checkerAllowance 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.CalculatorSavings and rental income taxSee how the 24%, 44% and 49% rates on savings interest and rental profit from 6 April 2027 change your Income Tax, against 2026/27.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.