- Home
- Insights
- GHG assurance
- Reasonable or limited assurance: choose before you procure
Reasonable or limited assurance: choose before you procure
Buyers often treat the level of assurance as a price point. It is not. It is a technical parameter agreed before planning that determines how much evidence is gathered, how deeply it is tested and, above all, how the conclusion may be worded. Choosing it after the quotation has been accepted is the wrong order.
What actually differs.
Reasonable assurance
The higher level- The verifier gathers evidence sufficient to reduce engagement risk to an acceptably low level.
- Substantive testing, larger and more targeted samples, recalculation, corroboration from independent sources.
- Controls are examined and, where relied upon, tested.
- Conclusion is expressed positively: the assertion is materially correct and conforms to the criteria.
- Normally required where the figure carries regulatory, financial or contractual consequence.
Limited assurance
The lower level- Evidence sufficient to reduce risk to a level that is acceptable, but higher than for reasonable assurance.
- Weighted toward enquiry and analytical procedures, with narrower substantive testing.
- Sampling is lighter and the work is materially smaller in scope.
- Conclusion is expressed negatively: nothing came to the verifier's attention indicating material misstatement.
- Appropriate for internal use, an early reporting cycle, or where the user has accepted the lower level explicitly.
Four questions that settle the level.
Who will rely on the figure, and for what?
A regulator, a European customer, a lender or a board committee relying on the number for a decision generally points to reasonable assurance. An internal baseline exercise may not.
UsersDoes any instrument specify a level?
A regulation, a disclosure framework, a loan covenant or a customer contract may name the level. Where it does, the choice has already been made and the question is only whether you meet it.
RequirementIs this the first cycle on this data?
First-cycle systems often cannot support reasonable assurance yet. Limited assurance in year one, with the findings used to close the gaps, is a legitimate and common path — provided the report says so.
MaturityWhat will the statement be used to say publicly?
If the organisation intends to make a public claim on the strength of the figure, the level of assurance behind it should be stated wherever the claim is made. A public claim on limited assurance that does not disclose the level is a reputational exposure.
Claim
Why the price gap is real.
Reasonable assurance costs more because it requires more evidence, not because it is a premium product. The additional effort sits in substantive testing, in wider sampling, and in the corroboration of data that limited assurance would examine analytically.
Where a proposal quotes reasonable assurance at a limited-assurance effort, the arithmetic has to break somewhere — and it breaks in the evidence file, which is exactly where an accreditation body looks during witness assessment. That is a risk to the client as much as to the body: a statement issued on insufficient evidence is a statement that can be withdrawn.
The defensible approach is to state the level, plan the evidence it requires, price that plan, and decline the engagement if the effort cannot be accommodated. We would rather quote a level you can afford honestly than sign a level we cannot evidence.
Primary sources
- ISO 14064-3:2019 — levels of assurance, materiality and evidence-gathering requirements — www.iso.org/certification.html (checked 01 September 2026)
- ISO 14065:2020 — requirements for validation and verification bodies — www.iso.org/certification.html (checked 01 September 2026)
- ISO/IEC 17029:2019 — general principles for validation and verification bodies — www.iso.org/certification.html (checked 01 September 2026)
- Commission Implementing Regulation (EU) 2025/2546 — CBAM verification principles and materiality levels — eur-lex.europa.eu/eli/reg_impl/2025/2546/oj/eng (checked 01 September 2026)
Editorial note. Author and technical review above are editorial functions. They are separate from the independent technical review and the decision functions required under ISO/IEC 17029:2019, which apply to validation and verification engagements and not to published articles. Nothing on this page is advice on a specific engagement, and nothing here extends or replaces the accreditation records.
Read next
Describe the claim — not the service.
Tell us what must be relied on, who will rely on it and by what date. We will confirm the correct programme, evidence requirement and responsible entity — or tell you it is outside our scope.