Practitioner Primer · Updated 18 May 2026
A plain-language primer on the engagement letter — the document that defines scope, fees, termination, and confidentiality, and that anchors your PII cover. Built for sole-practitioner and boutique tax agents in Australia.
Section 1 — The Why
An engagement letter is not optional paperwork. It is the contract between practitioner and client, the boundary of professional services performed, and — in practice — the limit of liability under most professional indemnity policies.
Issued by the Accounting Professional & Ethical Standards Board (APESB), APES 305 mandates that members of CA ANZ, CPA Australia, and the IPA document the terms of every engagement in writing before commencement of work. The accompanying APES 305-A guidance note provides drafting detail. Compliance is a condition of membership — and a routine focus of professional body quality reviews.
Registered tax agents are independently obligated under the Tax Practitioners Board (TPB) Code of Professional Conduct to provide tax-agent services competently, honestly, and within an agreed scope. The engagement letter is the most common evidence of that agreed scope when the TPB or a client disputes what was promised.
Most professional indemnity policies require an engagement letter to be in place at the time the work is performed. In claims, the absence of a signed engagement is one of the fastest paths to insurer denial — both because the scope is unprovable and because the limitation-of-liability clauses that the policy assumes are missing.
The three predictable failure modes when work commences without a signed engagement letter: scope expands silently (and unprofitably), the client disputes the final fee, and the PII insurer declines to defend any subsequent claim. Each is avoidable with a one-page signed letter on day one.
Section 2 — The Elements
APES 305 enumerates the matters that must be addressed in every engagement letter. Missing one is a finding in a professional body quality review — and a defect a court or PII insurer will seize on. Use this list as a drafting checklist before sending.
Specific services to be performed — not generic phrases like 'tax services'. The engagement letter must name the work product (e.g. '2025 Individual Income Tax Return for Ms J Smith').
Legal name(s), ABN/TFN where relevant, and the person with signing authority. For groups, list each entity separately or use a schedule attached to the cover letter.
Specific dates — typically a single financial year — not 'ongoing'. Open-ended engagements are an APES 305 red flag and a PII exposure.
Item-by-item list of deliverables. Anything not listed is out of scope. Bundling is fine ('preparation, lodgement, and one round of ATO follow-up'), but the boundary must be visible.
What the agent will do — preparation, lodgement, reasonable-care obligations under the TASA, professional standards compliance.
Provision of complete and accurate records, timeliness of information, signed declarations, and disclosure of all material facts.
Hourly, fixed, or retainer — and what triggers an out-of-scope variation. Disbursements, GST treatment, and payment terms.
Obligations under the Privacy Act 1988 and the Australian Privacy Principles. Cross-border storage disclosure if cloud accounting / cloud document storage sits offshore.
Start and end dates, notice periods either way, and conditions under which either party may terminate immediately.
Where allowable, a cap on liability under proportionate-liability statutes. Reference to the firm's complaints process and TPB / professional body escalation paths.
Declaration that the practitioner is independent of the client and free of undisclosed conflicts — and the process to disclose conflicts that arise mid-engagement.
This summary reflects APES 305 and APES 305-A as issued by the APESB. Always work from the current text of the standard at apesb.org.au — wording is periodically refreshed.
Section 3 — The Margin Killer
The most common reason tax agents fail to collect full fees isn't bad clients or slow lodgement — it's work performed outside an agreed scope, never re-priced, never billed. Tight, specific scope language in the engagement letter is the defence.
Each one consumes 15-30 minutes of partner / senior time. Ten across a year is a full billable day given away. Define email-correspondence inclusion explicitly (e.g. 'up to 30 minutes of incidental email correspondence per quarter').
Preparing the BAS is a compliance service. Advising on GST treatment of a new revenue stream is advisory. These are different services with different risk profiles and should be priced separately.
Routine ITR preparation does not include responding to ATO audit, review, or pre-issue contact. Carve it out explicitly: 'ATO correspondence beyond standard lodgement acknowledgement is priced separately'.
ITR review of a trust often surfaces missing resolutions, FBT obligations, or Division 7A issues. Each is a separate engagement deliverable, not a free fix.
Where a generic engagement might say “preparation of income tax returns”, a defensible engagement says: “preparation of the 2025 income tax return for [Entity] excluding any audit support, FBT advice, trust resolution drafting, or ATO correspondence beyond standard lodgement acknowledgement (each priced separately).” The exclusions do the heavy lifting — they turn every “quick question” into a re-pricing conversation rather than a quiet absorption.
Section 4 — Termination
Most engagement letters bury termination in a generic boilerplate paragraph. Done well, the termination clause gives both parties a clear, dignified exit — and protects the practitioner from continuing to carry risk for an unworkable client.
Either party may terminate on written notice. The market norm is 14 to 30 days, both ways. Clients retain the right to terminate at any time (consumer law); the practitioner's notice period is what is negotiable.
Engagements terminated mid-cycle still attract liability for the work already performed. PII run-off cover — typically 7 years post-termination — is the standard professional-body expectation. Don't drop the policy the day you wind up the engagement.
On termination, issue a handover letter — outgoing practitioner correspondence with the incoming agent, including a copy of working papers (subject to a lien for unpaid fees where permitted). A clean handover protects the client and limits residual disputes.
Section 5 — Fees
The engagement letter must state the basis of fees. Tax agents have specific constraints under the TPB Code that don't apply to other professions — most notably the restriction on contingent fees for compliance work.
| Structure | How it works |
|---|---|
| Hourly | Most accurate reflection of work done, but variable from the client's perspective. Best for advisory and one-off engagements. Always disclose the rate per role / seniority. |
| Fixed fee | Preferred by SME clients — but only viable when the scope is genuinely narrow and predictable. Build a variation mechanism into the letter for out-of-scope work. |
| Monthly retainer | Recurring fee for a defined scope (BAS preparation, payroll review, periodic check-ins). Define what is included and what triggers a variation. Renew the retainer annually. |
| Contingent / success-based | Prohibited for tax agents under the TPB Code of Professional Conduct in most situations — particularly where the fee depends on the size of a refund or tax outcome. Avoid entirely for compliance work. |
| Late payment terms | A standard term is 1.5% per month interest on overdue balances plus reasonable collection costs. Disclose this clearly in the engagement letter — not just on the invoice. |
| Pre-paid retainers | Funds received in advance of work performed are client monies. APES 310 (Dealing with Client Monies) sets out separate-account and reconciliation obligations. Don't co-mingle with operating funds. |
Pre-paid retainers received in advance of work are client monies and must be handled under APES 310 (Dealing with Client Monies). See apesb.org.au for the current text of APES 310.
Build (or buy) a standard engagement letter template with the APES 305 mandatory elements locked in. Then tailor only the scope and fee sections per client. The boilerplate (privacy, termination, dispute resolution) should not be re-drafted per engagement.
Issue a fresh engagement letter each financial year rather than carrying an open-ended engagement forward. Annual re-engagement resets dates, updates fees, refreshes consent to data handling, and creates a natural conversation about scope changes.
Two conditions that justify immediate termination on written notice: your PII cover lapses (you cannot lawfully continue to provide tax-agent services), or an unmanageable conflict of interest emerges. Don't try to ride either out.
The signed engagement letter belongs in the practice management system attached to the client record, with the acceptance date and the signing party recorded as structured data. Buried in someone's email, it can't be produced fast enough when it matters.
Yes — most Australian tax agents re-engage clients annually with updated dates and a refreshed fee schedule. APES 305 requires terms to be documented for each engagement, and a fresh letter is the cleanest way to reset the period, scope, and pricing. A 'standing' engagement letter that runs indefinitely is hard to defend if the work, fees, or contact people change.
APES 305 requires the terms to be agreed in writing before commencement of work. If the client refuses to sign, you do not have an engagement. Practically, many firms accept email confirmation ('I agree to the engagement letter dated X') as a written acceptance — but you need positive acknowledgement, not silence. Starting work without acceptance is the single largest contributor to fee disputes and PII denials.
You can include a limitation-of-liability clause, but its enforceability depends on proportionate-liability legislation in your state and on the terms of your PII policy. Many policies require certain language to preserve cover. Check with your professional body (CA ANZ, CPA Australia, or IPA) and your PII broker before drafting your standard clause — and never represent that your liability is more limited than it actually is.
An email exchange can satisfy the 'in writing' requirement under APES 305, but it must still cover the mandatory elements — scope, period, fees, responsibilities, confidentiality, and termination. Most firms use a PDF engagement letter attached to an email with an explicit 'reply YES to accept' instruction, then retain the reply in the practice management system. A bare email saying 'great, let's proceed' is not enough.
Any material change in scope, pricing, or parties. Examples: client acquires a new entity, a one-off advisory matter arises outside the compliance scope, the client requests work in a new service line (e.g. SMSF audit), the fee structure changes from hourly to fixed, or a key signatory changes. Issue a variation letter or a fresh engagement — do not absorb the change silently.
An engagement letter is the professional-practice document required by APES 305 and the TPB — it covers the specific accountancy/tax engagement, the period, and the practitioner's obligations under professional standards. A service agreement is a more general commercial contract often used for technology platforms, outsourced services, or multi-party arrangements. Tax agents typically need the engagement letter; some firms use both (engagement letter for the professional work plus a master services agreement for the broader commercial relationship).
OneBookPlus pairs APES-305-aligned engagement letter templates with scope tracking, fee variations, and time-recording — built for Australian tax-agent practices.
Last reviewed and updated: by Bishal Shrestha
About the author
Founder & CEO, OneBookPlus
Bishal has over a decade of experience in digital marketing, web development, and small business consulting across Australia. Bishal has reviewed APES 305 engagement letters and scope-creep clauses with Australian tax-agent practices across solo and multi-partner firms.
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