You’ve set group materiality at €500,000 for a holding company with four subsidiaries. You allocate €500,000 to each component. The aggregate of four individually immaterial misstatements (€400,000 each, all below component materiality) hits €1.6M at the group level. The group financial statements are materially misstated, and nobody’s individual work detected it. That is aggregation risk, and it is the reason ISA 600 (Revised) requires component materiality to be lower than group materiality.
ISA 600 (Revised), effective for periods beginning on or after 15 December 2023, requires the group engagement team to determine component performance materiality for each component where audit procedures are performed on disaggregated financial information. Component performance materiality must be set below group materiality to reduce the risk that the aggregate of uncorrected and undetected misstatements across components exceeds group materiality ( ISA 600 (Revised) para. 30).
Key takeaways
- Why ISA 600 (Revised) requires component materiality to be lower than group materiality, and what aggregation risk means in practice
- How to calculate component materiality using the 60-85% allocation range that most mid-tier firms apply
- How to adjust the allocation for components with different risk profiles, sizes, and reporting frameworks
- What the European Common Audit Inspection Methodology specifically checks in group audit files regarding materiality allocation
What ISA 600 (Revised) changed about component materiality
The previous version of ISA 600 used a classification model. Components were either “significant” (by financial significance or identified significant risk) or “not significant.” Materiality allocation followed from the classification. A significant component received a full-scope audit with component materiality set by the group engagement team. Non-significant components received analytical procedures or nothing.
ISA 600 (Revised) replaces this with a risk-based approach. The concept of “significant component” has been removed entirely. Instead, the group engagement team identifies and assesses risks of material misstatement at the group financial statement level first, then determines what work is needed at each component to respond to those assessed risks. The scoping decision is driven by risk, not by whether a component crosses a percentage threshold.
For materiality, the practical effect is that the group engagement team must now determine component performance materiality for every component where audit procedures will be performed on disaggregated financial information ( ISA 600 (Revised) para. 30). Under the old standard, a non-significant component subjected only to analytical procedures did not receive a formal component materiality. Under the revised standard, if audit procedures are performed at the component level, component performance materiality must be determined.
The ciferi ISA 600 guide covers the full scoping changes in detail. This post focuses specifically on the materiality allocation.
Aggregation risk: the concept that drives the calculation
Aggregation risk is the probability that the aggregate of individually immaterial uncorrected and undetected misstatements across components exceeds group materiality. ISA 600 (Revised) para. A78 explains that component performance materiality is set to reduce aggregation risk to an appropriately low level.
The concept is not new (it existed implicitly in the previous standard), but ISA 600 (Revised) makes it explicit. The more components a group has, the higher the aggregation risk, because each component can harbour a misstatement just below its own materiality threshold.
Consider a group with ten components, each allocated component materiality equal to group materiality. Each component could have an undetected misstatement of, say, 90% of group materiality. Ten such misstatements aggregate to nine times group materiality. The group financial statements would be massively misstated while every individual component file shows a clean result.
The fix is mechanical: set component materiality lower than group materiality. How much lower depends on the number of components and the degree to which the group’s financial information is disaggregated across them, combined with the assessed risk at each component. ISA 600 (Revised) does not prescribe a formula. It requires professional judgment. But the judgment must be documented and the reasoning must be traceable.
How to calculate component materiality in practice
ISA 600 (Revised) does not specify a calculation method. In practice, most mid-tier firms use a percentage of group materiality, adjusted for the number of components and their risk profiles. The common range is 60-85% of group materiality per component, with 75% being the most frequently applied starting point.
The percentage approach works like this. Start with group materiality (set under ISA 320 using the appropriate benchmark). Apply a component materiality percentage. The percentage is lower when there are more components (more aggregation risk) and higher when there are fewer components. Then set component performance materiality below component materiality, using the same approach as at the group level (typically 50-75% of component materiality).
A rule of thumb used by several mid-tier networks: for groups with two to four components, set component materiality at 75-85% of group materiality. For groups with five to ten components, set it at 60-75%. For groups with more than ten components, set it at 50-65%. These are starting points, not standards. The auditor must document why the chosen percentage is appropriate for the specific group.
An alternative approach (used by some firms) is the allocation method: divide group materiality across components based on their relative size, then apply a factor. For example, if a component represents 40% of group revenue, it receives 40% of group materiality, plus a buffer. This approach has a theoretical basis but creates practical problems when components are very unequal in size (a small component can receive a materiality so low that the audit becomes disproportionately expensive relative to the risk).
The percentage approach is simpler and easier to document. The ciferi materiality calculator supports both methods.
When to differentiate materiality across components
Not every component in a group carries the same risk. ISA 600 (Revised) para. A79 acknowledges that the group engagement team may determine different component performance materiality amounts for different components.
Reasons to set a lower component materiality for a specific component: the component has a significant risk identified at the group level (for example, a subsidiary with a complex revenue recognition arrangement), the component operates in a jurisdiction with a higher risk of fraud or non-compliance, the component has a history of misstatements identified in prior years, or the component is being audited by a component auditor whose work the group engagement team has less ability to direct and supervise.
Reasons to set a higher component materiality (closer to group materiality): the component is small relative to the group and the component’s financial information is straightforward (for example, a dormant holding entity). It also applies when the component is audited directly by the group engagement team with full access to all records.
The key documentation requirement: if different components receive different materiality amounts, the file must explain the differentiation. A flat percentage across all components is easy to document but may not reflect the actual risk profile. Differentiated percentages require more judgment and more documentation, but they produce a more defensible file.
The clearly trivial threshold at component level
ISA 600 (Revised) para. 30(b) requires the group engagement team to determine the threshold above which misstatements identified in the component financial information must be communicated to the group engagement team. This is the component-level equivalent of the “clearly trivial” threshold under ISA 450 .
In practice, this threshold is set at a percentage of component materiality (typically 5%, consistent with the group-level approach under ISA 450 .A2). Any misstatement at the component level above this threshold must be reported to the group engagement team for inclusion in the group schedule of uncorrected misstatements.
The European Common Audit Inspection Methodology specifically checks whether the group engagement team has documented the basis for determining both the component performance materiality and the communication threshold. If the file contains a component materiality figure but no documented rationale for the communication threshold, inspectors will flag it.
Worked example: Bakker Industrial B.V. group
Group profile: Bakker Industrial B.V. is a Dutch manufacturing holding company. The group consists of the parent entity and four wholly-owned subsidiaries: Bakker Machining B.V. (€32M revenue), Bakker Coatings B.V. (€18M revenue), Bakker GmbH (€12M revenue, German subsidiary), and Bakker Properties B.V. (€2M rental income, dormant investment property entity). Consolidated group revenue: €64M. Reporting framework: Dutch GAAP. All components audited by the group engagement team (no component auditors).
Set group materiality
Group materiality: €480,000 (0.75% of €64M consolidated revenue). Group performance materiality: €360,000 (75% of group materiality). Group clearly trivial threshold: €24,000 (5% of group materiality).
Documentation note: Record the benchmark (revenue) and the percentage (0.75%), with the rationale that profit fluctuates between years while revenue is stable. Cross-reference to the ISA 320 materiality working paper.
Determine component performance materiality
Four components. Moderate aggregation risk (four is a manageable number but two of the operating subsidiaries are individually material to the group). Starting point: 75% of group materiality.
Bakker Machining B.V.: component performance materiality of €340,000 (71% of group materiality). This is the largest subsidiary (50% of group revenue) with a significant revenue recognition risk (long-term manufacturing contracts with percentage-of-completion recognition). Set slightly below the 75% starting point to reflect the higher risk.
Bakker Coatings B.V.: component performance materiality of €360,000 (75% of group materiality). Standard risk profile, no individually significant risks identified beyond the group-level risks.
Bakker GmbH: component performance materiality of €310,000 (65% of group materiality). Lower allocation because the subsidiary operates in a different jurisdiction (Germany, HGB reporting converted to Dutch GAAP for consolidation), creating conversion risk, and the group engagement team has less direct familiarity with German regulatory requirements.
Bakker Properties B.V.: component performance materiality of €400,000 (83% of group materiality). The entity is a dormant property holding company with €2M rental income and minimal transactions. Risk is low. Setting materiality higher prevents disproportionate audit effort on an immaterial, low-risk entity.
Documentation note: Record the percentage applied to each component and the reasons for any differentiation from the starting point. Include the aggregation risk assessment. The sum of maximum possible undetected misstatements (one per component, each just below component performance materiality) is €1,410,000. This exceeds group materiality of €480,000, which is expected. The mitigation is that the probability of every component having an undetected misstatement at the maximum level simultaneously is low. Document this assessment.
Set communication thresholds
Each component’s communication threshold: 5% of the respective component performance materiality. Bakker Machining: €17,000. Bakker Coatings: €18,000. Bakker GmbH: €15,500. Bakker Properties: €20,000. Any misstatement above these thresholds at the component level is communicated to the group engagement team for the group schedule of uncorrected misstatements.
Documentation note: Record the threshold for each component. Include in the group audit instructions to each engagement team member responsible for the component.
Document and communicate
The group planning memorandum includes a component materiality table showing: component name, component revenue, percentage of group, component performance materiality amount, percentage of group materiality, and the communication threshold. This table is the single working paper that a reviewer needs to evaluate the allocation.
Documentation note: Cross-reference the component materiality table to the group ISA 320 working paper and the group audit instructions. If any component materiality is revised during fieldwork (for example, because a risk assessment changes), document the revision and the reason per ISA 600 (Revised) para. A80.
Practical checklist for component materiality
Common mistakes inspectors flag
- The European Common Audit Inspection Methodology specifically evaluates whether the group engagement team documented the basis for determining component performance materiality and the communication threshold. Files where component materiality equals group materiality (no reduction for aggregation risk) are a finding under ISA 600 (Revised) para. 30.
Related content
- Materiality glossary entry: Covers ISA 320 materiality at the entity level, which is the starting point for all component materiality calculations.
- Materiality calculator tool: The ciferi calculator includes a component materiality allocation module for groups with up to twelve components.
- ISA 600 : group audits complete guide: The full ciferi ISA 600 (Revised) guide, covering the risk-based scoping approach and two-way communications with component auditors, including the removal of the “significant component” concept.
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Frequently asked questions
What is aggregation risk in a group audit?
Aggregation risk is the probability that the aggregate of individually immaterial uncorrected and undetected misstatements across components exceeds group materiality. ISA 600 (Revised) para. A78 explains that component performance materiality is set to reduce aggregation risk to an appropriately low level. The more components a group has, the higher the aggregation risk, because each component can harbour a misstatement just below its own materiality threshold.
What percentage of group materiality should be used for component materiality?
ISA 600 (Revised) does not specify a percentage. In practice, most mid-tier firms use 60–85% of group materiality per component, with 75% being the most common starting point. For groups with two to four components, 75–85% is typical. For five to ten components, 60–75%. For more than ten components, 50–65%. These are starting points requiring professional judgment and documentation of why the chosen percentage is appropriate.
Can different components have different materiality levels?
Yes. ISA 600 (Revised) para. A79 acknowledges that the group engagement team may determine different component performance materiality amounts for different components. Reasons to set a lower amount include significant risks at the component level, higher-risk jurisdictions, or a history of misstatements. Reasons to set a higher amount include the component being small, low-risk, or dormant. If different components receive different amounts, the file must explain the differentiation.
What changed about component materiality in ISA 600 (Revised)?
The previous ISA 600 used a classification model where components were either "significant" or "not significant." ISA 600 (Revised), effective for periods beginning on or after 15 December 2023, replaces this with a risk-based approach. The concept of "significant component" has been removed entirely. The group engagement team must now determine component performance materiality for every component where audit procedures are performed on disaggregated financial information ( ISA 600 (Revised) para. 30).
What is the communication threshold at component level?
ISA 600 (Revised) para. 30(b) requires the group engagement team to determine the threshold above which misstatements identified in the component financial information must be communicated to the group engagement team. In practice, this is set at 5% of component performance materiality, consistent with the group-level "clearly trivial" threshold under ISA 450 .A2. Any misstatement above this threshold at the component level must be reported for the group schedule of uncorrected misstatements.
Further reading and source references
- IAASB Handbook 2024: the authoritative source for ISA 600 (Revised), including the application material on component performance materiality (paras. A78–A80).
- ISA 320 , Materiality in Planning and Performing an Audit: group materiality is set under ISA 320 before component materiality is determined.
- ISA 450 , Evaluation of Misstatements Identified during the Audit: the "clearly trivial" threshold concept that informs the component communication threshold.
- ICAS Implementation Guidance on ISA 600 (Revised): practical guidance on the transition from the "significant component" model to the risk-based approach.
- European Common Audit Inspection Methodology: the inspection framework that specifically evaluates component materiality documentation in group audit files.