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Using the Work of an Auditor's Expert (ISA 620)

Updated 11 October 2026 · Fact-checked

Under ISA 620, an auditor's expert is a person or firm with expertise outside accounting and auditing whose work the auditor uses to obtain evidence. You decide if one is needed, assess their competence, capabilities and objectivity, agree the scope in writing, then evaluate whether their work and findings are adequate. The auditor keeps sole responsibility for the opinion.

Understand Using the Work of an Auditor's Expert

Some audit areas need skills that auditors do not have. Examples are valuing a property portfolio, estimating oil reserves, assessing an actuarial pension liability or interpreting a complex legal contract. In these cases you may use an auditor's expert. This is an individual or organisation with expertise in a field other than accounting or auditing, whose work you use to help obtain sufficient appropriate audit evidence.

The expert can be internal to the audit firm, for example a firm's tax or IT specialist, or external, for example an independent valuer hired by the firm. This differs from a management's expert. That is someone engaged or employed by the client to help prepare the financial statements, such as the client's own valuer or actuary. You do not hire a management's expert. You treat their work as audit evidence and assess its reliability under ISA 500, and ISA 620 does not govern it.

The main principle is that the auditor alone is responsible for the audit opinion. Using an expert does not reduce that responsibility. The auditor cannot refer to the expert in an unmodified report. Only if a modified opinion arises from the expert's work, and the auditor feels it is relevant to understanding the modification, may reference be made. Even then it must be made clear this does not reduce responsibility. ISA 620 does not require the expert's consent for this, although you may wish to ask for their permission.

The process follows a logical order. First, decide whether an expert is needed, based on the nature and significance of the matter, the risk of material misstatement, and the availability of alternative evidence. Second, assess the expert's competence, capabilities and objectivity. Third, understand the expert's field. Fourth, agree the expert's role and scope. Finally, evaluate the adequacy of the work. Exam questions test each of these stages, often through a short scenario with a valuer, actuary or lawyer.

Key rules to remember

Definition of an auditor's expert: Auditor's expert = individual or organisation with expertise in a field other than accounting or auditing, whose work is used by the auditor to help obtain sufficient appropriate audit evidence; Can be internal (firm's own specialist) or external (hired by the firm).
Three evaluation factors: Competence + Capabilities + Objectivity; Competence is the nature and level of expertise. Capabilities is the ability to use that competence in the engagement circumstances. Objectivity is the risk of bias, conflict of interest or undue influence.
Information on competence and objectivity: Sources: personal experience of earlier work, discussions with the expert, discussions with other auditors, knowledge of qualifications and membership of a professional body, published papers or books, the expert's quality control policies; Useful checklist for written answers.
Matters to agree with the expert: Nature, scope and objectives of work; roles and responsibilities; nature, timing and extent of communication; need for the expert to observe confidentiality; Should be agreed in writing where appropriate.
Evaluating the work: Relevance and reasonableness of findings and conclusions; consistency with other evidence; assumptions and methods used; source data (relevance, completeness, accuracy); If the work is inadequate, agree further work with the expert or perform other procedures.
Responsibility rule: Responsibility for the audit opinion stays solely with the auditor; Do not refer to the expert in an unmodified report.

How to solve Using the Work of an Auditor's Expert questions

Use this order for any question on using an expert. Tie each point to the facts in the scenario, not to generic statements.

1Identify the matter needing specialist skill and say why the audit team cannot handle it, for example a complex valuation with high estimation uncertainty.
2Decide whether an expert is needed by looking at significance to the financial statements, risk of material misstatement and whether other evidence is available.
3Assess the expert's competence by looking at qualifications, membership of a professional body, experience and reputation.
4Assess capabilities and objectivity: can they do this work in the time and circumstances, and are there threats such as family ties, fees dependence or a link to management?
5Agree scope, roles, communication and confidentiality with the expert, preferably in writing.
6Evaluate the work: assumptions, methods, source data, reasonableness and consistency with other evidence.
7Conclude: if adequate, use it as evidence; if not, request more work or perform other procedures. State the auditor keeps responsibility for the opinion.
8Link to the report if relevant: no reference to the expert in an unmodified opinion.

Quickest way: Remember the sequence: Need, Assess, Agree, Evaluate

When to use it: Use when a question gives a short scenario and asks for matters to consider or procedures to perform with an expert, especially in Section B or C where time is tight.

Need: say what the specialist matter is and why an expert is needed.
Assess: write competence, capabilities, objectivity, each with one point linked to the scenario.
Agree: scope, roles, communication, confidentiality.
Evaluate: assumptions, methods, source data, consistency with other evidence.
Finish with one sentence: the auditor remains responsible for the opinion.

Common mistakes in Using the Work of an Auditor's Expert

Treating the client's own valuer or actuary as an auditor's expert and applying ISA 620.
The word expert looks the same in both cases, so students do not check who engaged the person.
Fix: Ask who engaged them. If management did, it is a management's expert and you evaluate their work as audit evidence under ISA 500. If the audit firm did, ISA 620 applies.
Saying the auditor can pass responsibility to the expert.
Students think hiring a specialist transfers the risk.
Fix: State clearly that the auditor alone is responsible for the opinion and that an unmodified report must not refer to the expert.
Listing only competence and forgetting capabilities and objectivity.
Competence feels like the obvious test, so the other two factors get skipped.
Fix: Always write all three headings and give one scenario-based point under each.
Giving a generic answer that ignores the scenario, such as 'check qualifications' for every case.
Students memorise lists without applying them.
Fix: Use scenario facts: for example, a valuer paid a fee linked to the reported value, or a valuer who is the director's relative, threatens objectivity.
Stopping after the expert's report is received.
Students forget the auditor must evaluate the work rather than accept it.
Fix: Add steps on assumptions, methods, source data and consistency with other evidence, and say what to do if the work is inadequate.
Confusing an auditor's expert with an internal auditor or with another auditor.
All three involve relying on other people's work.
Fix: Link each to its standard: ISA 620 for experts, ISA 610 for internal auditors, ISA 600 for component auditors. The expert's skill lies outside accounting and auditing.

Worked examples

Example 1

You are the audit senior on Zenith Ltd, which holds freehold properties that make up 60% of total assets and are carried at revalued amounts. The audit team has no valuation expertise. Explain whether you need an auditor's expert and what you would consider before using one.

Show the solution

Need: the properties are material at 60% of total assets and the revaluation involves significant estimation uncertainty. The team lacks valuation skills, so an auditor's expert is needed to obtain sufficient appropriate evidence.
Competence: check the valuer's professional qualifications, membership of a relevant professional body, experience of similar properties and locations, and reputation.
Capabilities: confirm the valuer can complete the work in the audit timetable and has the resources and local knowledge to value all the properties.
Objectivity: check for threats such as family or financial links to Zenith, fees dependent on the value, or previous work for management on the same properties.
Agree scope in writing: which properties, the valuation basis and date, the reporting format, communication and confidentiality.
Evaluate: review the assumptions and methods, test the source data given to the valuer, and compare the findings with other evidence such as market data and the client's valuation.
The auditor remains responsible for the opinion and must not refer to the expert in an unmodified report.

Answer: Yes, an auditor's expert is needed because the properties are material, the valuation is complex and the team lacks skills. Before using one, assess competence, capabilities and objectivity, agree scope in writing and evaluate the work. The auditor keeps responsibility for the opinion.

Example 2

Harbour plc has a defined benefit pension scheme. Its actuary, engaged by Harbour's directors, produced the pension liability figure. The auditor is considering whether to use this as evidence and whether ISA 620 applies. Explain.

Show the solution

Identify who engaged the actuary: Harbour's directors did, so this is a management's expert, not an auditor's expert.
Therefore ISA 620 does not apply to this actuary. The report is audit evidence, and the auditor evaluates its reliability under ISA 500, which includes assessing the actuary's competence, capabilities and objectivity.
Obtain an understanding of the actuary's work, the assumptions used (discount rate, mortality, salary growth) and the data supplied by management.
Evaluate the appropriateness of the actuary's work as audit evidence, including whether assumptions are reasonable and consistent with other evidence.
If the auditor lacks the skill to challenge the assumptions, the audit firm may engage its own actuary as an auditor's expert. In that case ISA 620 would apply to that expert.
The auditor remains responsible for the opinion in all cases.

Answer: The actuary is a management's expert, so ISA 620 does not apply to that work. The auditor evaluates it as audit evidence, and may engage a separate auditor's expert actuary, who would then be covered by ISA 620, if the team cannot assess the assumptions.

Exam tips

Always check who engaged the expert first. Auditor engaged means ISA 620. Management engaged means a management's expert, treated as audit evidence.
Write competence, capabilities and objectivity as separate headings, with a scenario-based point under each. This is where marks sit.
Do not forget to evaluate the expert's work. Name assumptions, methods and source data.
In objective test questions, watch for the trap options that say the auditor can refer to the expert in an unmodified report or that responsibility transfers to the expert. Both are wrong.
For Section C requirements asking for matters to consider, aim for one clear point per mark and tie it to the facts given.

Using the Work of an Auditor's Expert in other exams

The same ground in other exams, if you are preparing for more than one or want another angle on it.

Using the Work of an Auditor's Expert: frequently asked questions

What is the difference between an auditor's expert and a management's expert?

An auditor's expert is engaged or employed by the audit firm to help obtain audit evidence, and ISA 620 governs their use. A management's expert is engaged or employed by the client to help prepare the financial statements. The auditor treats their work as audit evidence and assesses its reliability.

When does an auditor need to use an expert?

You consider an expert when the matter needs skills outside accounting and auditing and the audit team lacks them. Typical examples are property valuations, actuarial pension calculations, mineral reserves and complex legal interpretations. The decision depends on the significance of the matter, the risk of material misstatement and the availability of other evidence.

How do I evaluate the competence and objectivity of an auditor's expert?

Competence covers qualifications, professional body membership and experience. Capabilities cover whether the expert can do the work in the circumstances. Objectivity covers bias, conflicts of interest and undue influence, such as family links or fees dependent on the outcome. Use experience of earlier work, discussions and published information as sources.

Can the auditor refer to the expert in the auditor's report?

Not in an unmodified opinion. If the opinion is modified and the work of the expert is relevant to understanding the modification, you may refer to the expert. Even then you must make clear that this does not reduce your responsibility. ISA 620 does not require the expert's consent, although you may wish to ask for permission.