COS Standards: What Dutch Auditing Standards Mean for Your Practice

What the NV COS actually is

The NV COS is not a separate set of auditing standards written from scratch. It is the Dutch transposition of the IAASB’s International Standards on Auditing, International Standards on Review Engagements, International Standards on Assurance Engagements, and International Standards on Related Services. The NBA adopts each IAASB standard with its effective dates and publishes it in Dutch with additional Dutch requirements where local law demands them.

Standaard 000N (the framework standard with the N suffix indicating it is Netherlands-specific) sets out how the entire NV COS structure works. Paragraph 16 explains that where Dutch-specific standards or paragraphs are needed, they are added to the relevant IAASB standard and printed in italics. Where an IAASB standard contains provisions that do not apply in the Netherlands, those provisions are simply omitted from the published Dutch version. This means you cannot always assume that the Dutch Standaard contains every paragraph from the corresponding ISA. The text you’re reading may be shorter.

The NV COS covers standards numbered 100 through 5699. Definitions that apply across multiple standards were previously in a separate glossary within the NV COS but were moved in 2022 to the HRA (Handleiding Regelgeving Accountancy) glossary, accessible at nba.nl. Individual standards still define terms specific to their own scope, and those definitions apply only within that standard unless stated otherwise.

For practitioners trained outside the Netherlands, the most important thing to understand is this: if you know the ISAs, you know approximately 90% of the NV COS. The remaining 10% consists of Dutch additions, Dutch-only standards, omissions of ISA provisions that conflict with Dutch law, and practice notes that interpret IAASB requirements for Dutch engagements. That 10% is where the review findings happen, and treating the Dutch additions as a tick box exercise rather than reading them is the fastest way to get there.

How the NV COS fits into the broader regulatory framework

The NV COS does not operate in isolation. It sits within a hierarchy of professional regulations that Dutch accountants must follow simultaneously.

At the top sits Dutch law: the Wet toezicht accountantsorganisaties (Wta) and the Besluit toezicht accountantsorganisaties (Bta) for firms performing statutory audits, and the Wet op het accountantsberoep (Wab) for all registered accountants. Below that sits the NBA’s professional regulation: the VGBA (ethical conduct), the VIO (independence), the NVKS (quality systems for firms), and the NV COS (engagement-level standards). The HRA (Handleiding Regelgeving Accountancy) contains the NV COS text and practice notes (handreikingen).

When a practitioner is deciding what standards to apply, the answer is always the NV COS plus the VGBA and VIO. NV COS tells you how to perform the engagement. VGBA governs ethical conduct, and VIO governs independence. All three are mandatory on every engagement. Practice notes (handreikingen, numbered from 1100 onwards) provide additional application guidance but do not carry the same mandatory weight as the standards themselves. Handreiking 1136 on compilation engagements and the revised Handreiking 1137 on corruption are among the most practically relevant for mid-tier firms.

How the NV COS maps to the ISAs

The mapping is deliberate and direct. Standaard 200 corresponds to ISA 200 . Similarly, 315 maps to ISA 315 (Revised 2019), 540 maps to ISA 540 (Revised), and 700 maps to ISA 700 . The numbering is identical throughout. When the IAASB revises a standard, the NBA adopts the revised version with the same effective date unless Dutch law requires a different implementation timeline.

The NBA has adopted ISA 250 (Revised) and ISA 540 (Revised) and incorporated mandatory training on both into its member programmes. For the upcoming revised standards effective December 2026 ( ISA 240 Revised, ISA 500 Revised, ISA 570 Revised, and the related conforming amendments), the NBA will follow the same adoption pattern. Dutch practitioners should monitor nba.nl/wet-en-regelgeving for publication of the Dutch text, as the translation and addition of Dutch-specific requirements can take several months after the IAASB issues the final standard.

Where the standards diverge from the ISAs, the divergence is always flagged. Dutch-specific text appears in italics in the body of the standard. Dutch-specific standards carry the N suffix (Standaard 000N, Standaard 3950N, Standaard 4415N, Standaard 4416N). A practitioner reading a Dutch standard can therefore distinguish at a glance between text that originates from the IAASB and text that originates from the NBA. This typographic convention is not decorative. It tells you which requirements exist only in the Netherlands and which are internationally recognised.

What the December 2026 revised standards mean for the NV COS

The IAASB is issuing revised versions of ISA 240 (Fraud), ISA 500 (Audit Evidence), and ISA 570 (Going Concern), all effective for periods beginning on or after 15 December 2026. The NBA will adopt these as revised Standaarden with the same effective dates, following its standard adoption process.

For Dutch practitioners, the revised standards will arrive with Dutch-specific additions that don’t yet exist. The NBA must review each revised ISA, determine where Dutch law or practice requires additional requirements, draft those additions, and publish the Dutch text. This process takes time. The practical implication: do not assume that the final IAASB text equals the final Dutch text. Wait for the NBA’s published version before updating your firm’s templates and work programmes.

ISA 240 Revised is particularly significant because the AFM has flagged fraud risk identification as a recurring concern in its inspection findings. The revised standard changes the auditor’s default posture toward fraud risk, and the NBA may add further Dutch-specific requirements given the recent examination fraud scandals and the AFM’s thematic focus. Firms that start preparing for ISA 240 Revised now should build flexibility into their planning, because the final Dutch Standaard may go further than the IAASB text.

The standard series and what each covers

The NV COS is organised into series by engagement type. Knowing which series applies to your engagement is the first step in scoping the applicable standards.

Standaarden 100 to 999 cover the audit of financial statements (controle van financiële overzichten). This is the series you work with for statutory audits under the Wta and for voluntary audits. It includes the core audit standards you already know from your ISA training: risk assessment (Standaard 315), materiality (Standaard 320), responses to assessed risks (Standaard 330), audit evidence (Standaard 500), the auditor’s report (Standaarden 700 to 799), and everything in between.

Standaard 2400 covers review engagements for historical financial information (beoordelingsopdrachten). If your firm performs review engagements rather than full audits (common for entities below the statutory audit threshold that want some level of assurance), this is the governing standard. A review provides limited assurance, expressed as negative assurance (“nothing has come to our attention”), compared to the reasonable assurance of a full audit. The distinction affects the nature and extent of procedures and the wording of the practitioner’s report.

Standaarden 3000A and 3000D cover other assurance engagements (overige assurance-opdrachten). The “A” variant applies to attestation engagements; the “D” variant applies to direct reporting engagements. Attestation engagements involve a subject matter that the responsible party has measured or evaluated, while direct reporting engagements involve the practitioner performing that measurement. ISAE 3402 engagements (service organisation controls) fall under the 3000-series. With the growth of the Dutch SaaS and service organisation market, this series is becoming increasingly relevant for mid-tier firms.

Standaard 4410 covers compilation engagements (samenstellingsopdrachten). This is the standard most frequently relevant for smaller Dutch practices that prepare financial statements for clients without providing assurance. A compilation engagement does not result in an opinion or a conclusion; the practitioner assists in preparing the financial statements and reports on that engagement. Related Dutch-specific standards include Standaard 4415N and 4416N, which address particular Dutch requirements. For many accountancy practices outside the statutory audit segment, Standaard 4410 and its Dutch supplements are the standards they work with daily.

Standaarden in the 5000-series cover specialist areas. Standaard 3950N, which governs the auditor’s approach to SBR reporting, sits in the broader regulatory standards area. The 800-series covers special considerations for audits of financial statements prepared under special purpose frameworks. Smaller firms may encounter the 800-series when auditing subsidy reports or special-purpose financial statements required by grant providers.

Dutch-specific additions: how to spot them in the text

Four signals tell you that a requirement is Dutch-only.

First: italicised text within a standard. Wherever the NBA has added requirements beyond the IAASB text, those additions appear in italics. For example, Standaard 700 contains Dutch-specific requirements for the content and format of the auditor’s report that reflect Dutch law and NBA regulations. These italicised paragraphs carry the same authority as the rest of the standard. Failure to comply with an italicised requirement is treated identically to failure to comply with an IAASB-originating requirement during an AFM inspection or NBA quality review. A firm that argues “but the ISA doesn’t require this” will find that the argument holds no weight when the Dutch standard does require it.

Second: paragraphs with a letter suffix after the number. When the NBA inserts additional application guidance into an existing IAASB standard, the new paragraph receives the next sequential paragraph number followed by a letter (for example, A51A). This preserves the original IAASB paragraph numbering while making the Dutch addition identifiable. In practice, this means that if you are comparing the Dutch text to an English-language ISA to check a specific paragraph reference, you may find paragraphs in the Dutch version that don’t exist in the international version. They are not errors. They are additions.

Third: entire standards with the N suffix. These are standards that exist only in the Netherlands. When you encounter an N-suffix standard, there is no international equivalent to reference. The framework standard 000N explains the overall structure. Standards 4415N and 4416N add Dutch-specific compilation requirements. And 3950N governs the SBR audit approach.

Fourth: practice notes (handreikingen) that interpret IAASB standards for Dutch practice. These are numbered from 1100 onward and appear in the HRA alongside the standards. Handreiking 1136 on compilation engagements is a common example. Practice notes don’t carry the same mandatory weight as standards, but the NBA’s quality reviewers treat them as the expected application baseline.

Standards that have no ISA equivalent

Several standards in the NV COS address matters that are unique to Dutch law or Dutch reporting practice.

Standaard 3950N is perhaps the most practically significant Dutch-only standard. It governs how auditors approach the audit of financial statements that will be filed electronically through SBR (Standard Business Reporting) in XBRL format. Under Standaard 3950N, the auditor must verify that the XBRL instance accurately reflects the audited financial information, that the correct taxonomy elements have been applied, that the digital auditor’s report is properly linked and signed, and that the filing is complete before submission. With the 2025 expansion of mandatory SBR filing to large entities, Standaard 3950N applies to a growing number of audit engagements.

Standaard 4415N and 4416N supplement Standaard 4410 (compilation engagements) with Dutch-specific requirements. Given that compilation engagements represent the majority of work at many smaller Dutch practices, these standards directly affect day-to-day file documentation. Handreiking 1136 (Practice Note 1136) provides additional guidance on applying NV COS 4410 in Dutch practice and is the document most commonly referenced during NBA quality reviews of compilation files.

The VGBA (Verordening Gedrags- en Beroepsregels Accountants) and VIO (Verordening inzake de Onafhankelijkheid) sit alongside the NV COS as mandatory professional regulations. While not technically “standards” in the NV COS numbering, they carry equal authority and are tested during both AFM inspections and NBA quality reviews. The VGBA covers ethical conduct; the VIO covers independence. Every practitioner must comply with both on every engagement.

Worked example: Vermeer Audit Partners applies the right standards to a new engagement

Scenario: Vermeer Audit Partners B.V. is a five-partner firm in Den Haag with an AFM Wta licence. A new client, Mulder Vastgoed B.V., has €22M in assets, €18M in net revenue, and 38 employees. The client previously had a compilation engagement with another firm and now wants a statutory audit for the first time because a bank requires it for a new credit facility.

Determine the engagement type

Mulder Vastgoed meets two of the statutory audit criteria (assets above €7.5M and revenue above €15M). However, the company has fewer than 50 employees, so it meets only two of the criteria on the current balance sheet date. The engagement partner checks the prior year: assets were €19M, revenue was €16M, and employees were 35. Two criteria met on two consecutive dates. Statutory audit required.

Documentation note: record the size criteria assessment in the engagement acceptance file with both current and prior year figures. Reference Article 393(1) of Book 2 of the Dutch Civil Code.

Identify the applicable standards

Because this is a statutory audit, Standaarden 100 to 999 apply in full. The engagement partner maps the key standards: Standaard 210 (engagement terms), Standaard 220 (quality management at the engagement level), Standaard 315 (risk identification and assessment), Standaard 320 (materiality), Standaard 330 (responses to assessed risks), Standaard 500 to 580 (evidence), Standaard 700 (auditor’s report).

Because Mulder Vastgoed’s financial statements will be filed through SBR in XBRL format, Standaard 3950N also applies. The engagement team must plan for the SBR-specific procedures at the completion stage.

Documentation note: include the list of applicable standards in the planning memorandum. Flag Standaard 3950N specifically, as this may be the firm’s first engagement where the client falls under the expanded SBR mandate for large entities.

Check for Dutch-specific requirements

The engagement partner reads Standaard 700 with attention to the italicised paragraphs. The Dutch auditor’s report format has specific requirements for the management board report (bestuursverslag) opinion and the statutory references that differ from the generic ISA 700 report. The firm’s template auditor’s report must match the Dutch format, not the international format.

Documentation note: verify the firm’s auditor’s report template against the current NBA model auditor’s report (modelverklaring). The NBA updates this template when standards or law change.

Consider the VIO and VGBA

The VIO requires a specific independence assessment for this new engagement, including a check for any prior relationships between the firm and the client. Because one of Vermeer’s partners previously provided tax advisory services to Mulder Vastgoed’s director personally, the engagement partner documents this relationship and assesses whether it creates a threat to independence under VIO Article 16.

Documentation note: record the independence assessment in the acceptance file. If the prior tax relationship creates a self-interest threat, document the protective measure applied (separate teams, different partner, time elapsed since the advisory work).

Practical checklist

The common thread across these checks: the file should tell a story that shows you knew which standards applied, including the Dutch-specific ones, and that you applied them deliberately rather than by accident.

Common mistakes

• Treating compilation engagements as if Standaard 4410 is the only applicable standard. Standaarden 4415N and 4416N add Dutch-specific requirements, and Handreiking 1136 is the primary reference document the NBA’s Raad voor Toezicht uses when reviewing compilation files.
• Overlooking Standaard 3950N for engagements where the client files through SBR. With the 2025 expansion of mandatory SBR filing to large entities, this standard now applies to a larger share of statutory audit engagements than in previous years.
• Assuming the NBA adopts revised ISAs on the same date as the IAASB. In our experience, adoption dates usually land within a few months of each other, but the NBA’s translation and Dutch-addition process can push the Dutch publication out by several months beyond the IAASB effective date. Using the IAASB text before the NBA publishes the Dutch version risks missing Dutch-specific requirements.

Related content

• Glossary: NV COS (Nadere Voorschriften Controle- en Overige Standaarden). Explains the Dutch auditing standards framework and its relationship to the international ISAs.
• ISA 520 Analytical Review Calculator. Supports the analytical procedures required under Standaard 520.
• SBR reporting in the Netherlands. Covers the SBR filing requirements and Standaard 3950N in detail.

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Frequently asked questions

Further reading and source references

• The NBA HRA (Handleiding Regelgeving Accountancy) contains the NV COS text, practice notes, and supporting guidance. Available at nba.nl.
• Standaard 000N is the framework standard explaining how the NV COS structure works and how Dutch additions are identified.
• The IAASB Handbook 2024 provides the international source text for comparison with the Dutch transposition.
• Handreiking 1136 offers practical guidance on applying NV COS 4410 for compilation engagements in Dutch practice.