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For the 31 January run

A Self Assessment engagement letter written for 31 January

Every practice knows what January looks like. The Self Assessment letter is where you decide, in September, what the client owes you before it starts.

A Self Assessment client thinks of "my tax return" as one thing. It is an SA100 and whichever supplementary pages their year needed — employment, self-employment, property, capital gains, foreign income — and possibly a 60-day property return that has nothing to do with 31 January at all.

Free download

Self Assessment engagement letter

The full letter in Word and PDF for UK practices, with the payments on account, enquiry and anti-money laundering clauses.

Download the PDF Download for Word

No email required.

Use the free engagement letter generator

Type in your firm, the client, the scope and the fee, and it writes a complete engagement letter for the United Kingdom, ready to print or save as a PDF. Nothing you type is stored.

Next step: send it to the client through FirmHello, where it stays on their record beside everything else they send you.

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Since April 2026 there is a second complication: clients whose self-employment and property income crossed the Making Tax Digital threshold now report quarterly, and their year-end return runs through software. They need a different schedule, and the letter should say which kind of client this is.

What a Self Assessment letter has to settle

Five clauses do most of the work. The rest of the letter is the terms of business every engagement shares.

  1. 1

    Which pages, for which tax year

    Name the tax year and list the pages you will prepare: SA102 employment, SA103 self-employment, SA105 property, SA106 foreign, SA108 capital gains. Say that a 60-day return for a UK residential property disposal is a separate service unless the letter includes it.

  2. 2

    The client approves the return before it goes

    HMRC expects the agent to have the client's confirmation before a return is submitted. Write down how it is given — a signed approval, or a recorded confirmation in your portal — and that nothing is filed without it.

  3. 3

    Payments on account, explained once

    The balancing payment and the first payment on account are due on 31 January, the second on 31 July. Clients who are new to them are surprised twice. Say who calculates them and who pays them.

  4. 4

    Enquiries are extra

    If HMRC opens an enquiry into the return, dealing with it is not part of the preparation fee. Say how it is charged, and mention fee protection insurance if you offer it.

  5. 5

    Anti-money laundering, in plain terms

    You must carry out client due diligence under the Money Laundering Regulations 2017, and you may be required to report a suspicion to the National Crime Agency without telling the client. The letter is where the client hears that first.

The Self Assessment engagement letter

Written for United Kingdom. The downloads are the same text, as a Word document to edit and a PDF to put on your letterhead.

[Firm letterhead]

[Date]

[Client name]
[Client address]

Dear [Client name],

The engagement

We will prepare your Self Assessment tax return (SA100) for the tax year ended 5 April [year], with the supplementary pages for [employment / self-employment / property income / foreign income / capital gains], and submit it to HM Revenue & Customs once you have approved it. We will calculate your tax liability and any payments on account, and tell you what to pay and when.

What is not included

This engagement does not include returns under Making Tax Digital for Income Tax, which are covered by a separate schedule; 60-day returns for UK residential property disposals; returns for any other person; bookkeeping; tax planning or advice; or dealing with any enquiry or compliance check that HMRC opens into your return. We will agree any of these with you separately.

Your responsibilities

You are legally responsible for your tax return and for making sure it is correct and complete, even though we prepare it. You will give us all the information we need by [date], tell us about any new source of income, and keep the records that support your return for the period the law requires — at least five years after the 31 January filing deadline if you are self-employed or let property.

We will send you the completed return to review. We will not submit it until you have confirmed to us, [in writing / in our client portal], that it is correct and complete.

Deadlines and payments

The online filing deadline is 31 January following the end of the tax year. Any balancing payment and your first payment on account for the following year are due on the same date, with a second payment on account due on 31 July. If information reaches us after [date] we cannot guarantee to file by 31 January, and HMRC's penalties for late filing and late payment would apply.

Authority to act

You authorise us to act as your agent with HMRC for Self Assessment. We will request this through HMRC's online agent authorisation. HMRC will continue to correspond with you directly on some matters; please send us anything you receive from them.

Anti-money laundering

We are required by the Money Laundering Regulations 2017 to verify your identity and to keep evidence of it. We are also required to report to the National Crime Agency if we know or suspect money laundering, and the law may prevent us from telling you that we have done so.

Fees

Our fee is [amount] plus VAT, invoiced when the return is ready for your approval and payable within [number] days. Work outside this scope, including any HMRC enquiry, is charged at [rate] per hour and agreed with you first.

Your data

We process your personal data in accordance with the UK GDPR and the Data Protection Act 2018, as described in our privacy notice, and retain our files for [number] years.

Agreement

This letter and our standard terms of business form our contract. Please sign and return a copy.

Yours sincerely,
[Name], [Firm name]

Agreed by [Client name]:

Signature ______________________ Date ____________

Before you use this

Supplied as-is, with no guarantee. These templates are general information, not legal advice, and not a substitute for it. Have your own legal adviser review and adapt one to your practice and your jurisdiction before you put it in front of a client. FirmHello accepts no responsibility or liability for any use made of them.

Where Self Assessment engagements go wrong

The property sale in October

A client sells a buy-to-let and mentions it in January. The 60-day return was due months earlier. Name the service and its trigger, and ask the question in the letter.

Filed on an "all fine"

A one-line email reply is thin evidence that the client reviewed the return. A recorded approval, against the version they actually saw, is not.

The July surprise

The second payment on account arrives as news every year. One sentence in the letter, and one in the covering note, prevent the phone call.

Other engagement letters

Making Tax Digital Making Tax Digital Tax preparation Tax preparation Template and samples Templates

Questions about Self Assessment engagement letters

Do I need a new letter each tax year?

Not necessarily — many firms issue one letter with an annual schedule of services. What matters is that the letter describes the work you are actually doing, and it should be reissued when that changes, such as when a client comes within Making Tax Digital.

Is a 64-8 still how clients authorise an agent?

HMRC's online agent authorisation through the Agent Services Account is the usual route. The paper 64-8 is now accepted only for full authorisation, not limited authorisation.

Should the letter cover HMRC enquiries?

It should mention them, to say they are outside the standard fee. An enquiry can take more time than the return did, and a client who was never told that will expect it to be included.

What if the client is now in Making Tax Digital?

Then their obligations are quarterly updates plus a year-end return filed through software, and they need the MTD schedule instead of, or as well as, this one. See the Making Tax Digital engagement letter.

What changed

  • Added an editable Word (.docx) copy of the letter beside the PDF.

The letter is the easy half

Sending it, getting it back signed, and finding it again in two years is the half that eats the week. That is what the portal is for.

No card and no sales call. If you would rather tell us about your firm first, use the longer form.