Dutch Audit Market: How the Non-Big 4 Sector Actually Works

How the Dutch audit market is structured

The Netherlands has two categories of audit firm licence. OOB-accountantsorganisaties (currently six firms: Deloitte, EY, KPMG, PwC, BDO, and Mazars) hold licences to audit public interest entities (organisaties van openbaar belang). Reguliere vergunninghouders hold AFM licences to perform statutory audits of non-PIE entities. As of 2024, there are approximately 224 reguliere vergunninghouders, though this number has been declining gradually as smaller firms merge or exit.

The distinction matters because it determines your supervision regime. OOB firms face direct, continuous AFM inspection of individual audit files. Reguliere vergunninghouders face AFM supervision for their statutory audit work but fall under the NBA’s Raad voor Toezicht for non-statutory assurance, compilation, and review engagements. Both types of firm must comply with the Wet toezicht accountantsorganisaties (Wta) and the Besluit toezicht accountantsorganisaties (Bta). If you work at a reguliere vergunninghouder that also performs non-statutory assurance work, your firm answers to two different supervisors for two different categories of engagement.

Below the AFM-licensed tier sits a much larger group: accountancy practices that perform no statutory audits at all but carry out compilation engagements and voluntary reviews. These firms hold no AFM licence and fall exclusively under the NBA’s six-yearly toetsing cycle. The total accountancy profession in the Netherlands includes over 22,000 NBA members, but only a fraction work at firms that perform statutory audits.

Dutch statutory audit thresholds (as of financial year 2024) require an audit when a company meets at least two of the following on two consecutive balance sheet dates: assets exceeding €7.5 million, net turnover exceeding €15 million, or more than 50 employees. These thresholds were increased by 25% in March 2024 following the European Commission’s adjustment. For mid-tier audit firms, this threshold increase has a direct pipeline effect: some previously audit-obligated companies now fall below the threshold, which means fewer mandatory engagements in the pipeline for the firms that were auditing them. The AFM explicitly noted in Sector in Beeld 2025 that the term “MKB” (SME) is sometimes incorrectly used in relation to statutory audits. Small enterprises are not subject to mandatory audit. The mandatory audit requirement starts at what the Dutch classification considers “medium-sized.”

The numbers: what the AFM reports about mid-tier growth

The AFM’s Sector in Beeld 2025 report provides the clearest picture of how the Dutch audit market is shifting. Total statutory audit revenue for non-PIE clients grew from €678 million in 2014 to €1,485 million in 2024. Reguliere vergunninghouders captured a disproportionate share of that growth, moving from 18% to 40% market share over the same period.

Also from Sector in Beeld: 54% of statutory audits performed by reguliere vergunninghouders are now fully data-driven (gegevensgericht). This number has been increasing steadily, reflecting both the adoption of data analytics tools and the standardisation of Dutch financial data through SBR/XBRL reporting. For firms considering technology investment, this is not a future trend. More than half of your competitors are already there.

Incident reporting tells a more complicated story. In 2024, the AFM received 56 incident notifications from audit firms: 18 from OOB firms and 38 from reguliere vergunninghouders. The higher absolute number from mid-tier firms partly reflects the larger number of firms in this category, but the AFM flagged the increase from 2023 (when reguliere vergunninghouders reported 27 incidents) as notable. Whether this increase reflects more incidents or better reporting discipline is unclear from the published data.

Fraud risk identification also varies by firm size. The AFM observed that small reguliere vergunninghouders have the lowest percentage of statutory audits with more than two identified fraud risks. At OOB firms, the share of audits identifying more than two fraud risks rose from 42% in 2023 to 47% in 2024. The AFM’s position is direct: insufficient follow-up on identified fraud risks puts the profession’s gatekeeping role under pressure. Nobody enjoys the fraud risk discussion at smaller firms, where you know the owner-manager personally and the conversation feels adversarial. But this is exactly the area generating the most review notes. The NBA responded to these findings by stating that identifying risks is only the first step; it matters whether firms then determine if those risks actually materialise and whether mitigations are adequate.

Consultation rates differ too. About 32% of statutory audits at reguliere vergunninghouders included consultations with internal specialists in 2024, compared to 25% at OOB firms. The most common consultation topics across all firm types were the auditor’s report, going concern, independence, and fraud. At non-PIE firms specifically, auditor’s report questions topped the list (26.7% of consultations), which suggests that smaller firms seek more guidance on how to express their conclusions than on how to perform the underlying work.

Who regulates what and how the supervisory bodies interact

If you work at a mid-tier firm, you answer to multiple supervisors, and the way they interact confuses most practitioners.

The AFM supervises all firms holding a Wta licence for their statutory audit work. This includes thematic investigations (the 2025 fraud risk investigation is a recent example), desk reviews of reported financial statements, monitoring of incident reports, and data collection through the annual market monitor. The AFM does not conduct file-by-file inspections of every reguliere vergunninghouder every year. Its supervision is risk-based and thematic.

The NBA’s Raad voor Toezicht supervises quality for non-statutory work: voluntary audits, review engagements, compilation engagements under NV COS 4410 , and other assurance work. This is the six-yearly toetsing cycle with its new mid-cycle development conversation. In 2024, the Raad reviewed 183 firms (together with the SRA) and found a 76% pass rate. The previous year, with a different cohort, the pass rate was 64%. We’ve seen firms treat the toetsing as a tick box exercise and then scramble when the pass rate comes in lower than they expected.

The SRA sits in a different position entirely. It is not a regulator. It is a network organisation representing over 370 independent SME-focused accounting and audit firms. Approximately 70% of all reguliere vergunninghouders are SRA members, according to the SRA. The organisation provides practical support: quality programmes, model handbooks, peer review services, and collective lobbying on regulatory matters. It is also accredited by the NBA’s Raad voor Toezicht to conduct quality reviews in the NBA domain, which means SRA staff review member firms under delegation from the professional body that sets the standards those firms must meet.

This creates an unusual tension. The SRA represents the firms that the NBA reviews, and simultaneously conducts some of those reviews on the NBA’s behalf. When the NBA sent letters to reguliere vergunninghouders about exam fraud investigations in 2024, SRA chair Diana Clement publicly questioned the NBA’s mandate and suggested the professional body did not fully understand the operating reality of smaller firms. Specifically, Clement argued that many of the exams implicated in the Big 4 fraud scandals are not even required at smaller firms, making the NBA’s blanket approach disproportionate. NBA chair Kris Douma responded that reguliere vergunninghouders are well represented on the NBA board and that the professional body was acting within its quality-protection mandate. This tension between the professional body and the network organisation is a persistent feature of the Dutch mid-tier market.

The service organisation model

Most mid-tier and smaller audit firms in the Netherlands do not build their entire quality infrastructure from scratch. They subscribe to a service organisation (serviceorganisatie) that provides standardised audit methodologies, quality handbooks, template files, and ongoing technical support. The major service organisations serving reguliere vergunninghouders include Novak, Auxilium, Fiscount, and Extendum.

AFM data shows that in 2024, 54% of non-PIE audit firms used professional practice support from the SRA, up from 45% in 2021. An additional 20% used support directly from the NBA, up from 17% in 2021. These numbers reflect a market where independent quality infrastructure is the exception, not the norm. For a firm with two or four partners performing statutory audits alongside compilation and advisory work, building bespoke audit methodology is not practical.

Service organisations also play a role in NBA quality review preparation. Several offer pre-review services: a simulated toetsing where a consultant walks through the orientation questionnaire and inspects sample files before the real reviewer arrives. The practical value depends on whether the firm treats it as a genuine diagnostic or as a last-minute fix. Reviewers look for whether the file tells a story (consistent documentation that builds logically from planning through to conclusion). The Raad voor Toezicht can see from documentation dates which improvements were made years before the review and which were made weeks before.

For firms evaluating whether to join a service organisation, the calculation is straightforward. Building your own audit methodology, maintaining your own handbook, and keeping your own templates current requires dedicated vaktechniek capacity that most two-to-five partner firms don’t have. Service organisation membership typically costs between €5,000 and €15,000 annually depending on firm size. A failed NBA review triggers improvement plan costs that run significantly higher, plus the reputational and operational disruption of a re-review cycle.

Worked example: how supervision plays out for Bakker & Partners

Scenario: Bakker & Partners Accountants B.V. is a seven-partner firm in Utrecht with €3.2M revenue. Four partners hold RA qualifications. The firm performs 45 statutory audits per year (non-PIE), plus approximately 120 compilation engagements and 15 voluntary reviews. It holds an AFM Wta licence and is an SRA member.

AFM supervision (statutory audit work)

The AFM requires Bakker & Partners to submit annual data through the market monitor. In 2024, the firm reported two early terminations of audit engagements and one incident notification (a client reporting suspected management fraud after year-end). The AFM logged the incident and may follow up with a desk review of the firm’s response. The AFM’s thematic investigation on fraud risk identification results in a questionnaire that Bakker & Partners must complete, documenting how fraud risks are identified and followed up across a sample of statutory audit files.

Documentation note: retain copies of all AFM submissions and responses. The AFM’s risk profile for your firm builds cumulatively across years.

NBA Raad voor Toezicht (non-statutory work)

Bakker & Partners was last reviewed in 2021 and received a pass with recommendations. Under toezicht op nieuwe leest, the firm had its first development conversation in March 2024. The team leader discussed the quality evaluation outcomes for 2022 and 2023 and the firm’s approach to the NVKS monitoring requirements. No formal findings resulted. The next full toetsing is scheduled for 2027.

Documentation note: the development conversation is not graded, but the team leader who conducted it will lead the 2027 review. Impressions formed during the conversation carry forward.

SRA membership

Bakker & Partners uses SRA’s standardised audit methodology and quality handbook. When the AFM’s fraud risk report was published in January 2025, the SRA organised a session with affected member firms and the AFM to discuss findings. The SRA announced it would update its practical guidelines and work programmes based on the investigation results.

Upcoming regulatory changes for mid-tier firms

Under the Wijzigingswet accountancysector (the legislative reform bill for the audit sector), several changes are coming for reguliere vergunninghouders, though not all will apply immediately.

Quality reporting through audit quality indicators (AQIs) will initially apply only to OOB firms. Minister Heinen stated in May 2025 that the reporting obligation for reguliere vergunninghouders will not be introduced until after a three-year evaluation of how it works at OOB firms. This buys time, but it also signals the direction of travel.

Stricter internal governance requirements will apply to the 15 to 20 largest reguliere vergunninghouders. These firms will need to establish or strengthen internal supervisory structures, modelled on the structuurregime governance approach. For mid-tier firms below this threshold, the requirement does not apply directly, but the Raad voor Toezicht may incorporate governance questions into its review process regardless. The distinction between “legally required” and “practically expected” matters less than most firms think.

Minister Heinen also deferred the NBA’s proposed aanwijzingsbevoegdheid (the power to assign auditors to PIE entities that cannot find one), citing no current evidence of a problem. According to Heinen’s letter, reguliere vergunninghouders currently handle approximately 60% of all statutory audits, while the six OOB firms cover about 40%, a share that is slowly declining. This market composition makes the assignment power a loaded instrument, and the minister clearly preferred to keep it in reserve rather than activate it.

Private equity involvement in audit firms is a growing concern for the Raad voor Toezicht. In its 2024 report, the Raad noted that determining how voting rights are structured in PE-backed firms is sometimes difficult, and that several final review opinions were delayed pending clarification. As a result, private equity was added as a topic in the 2025 monitoring questionnaire. The AFM also flagged PE involvement in its 2023 Sector in Beeld report, noting that while PE capital can bring advantages (technology investment, operational professionalisation), the regulator currently weighs the risks more heavily. Those risks include pressure on fee levels and incentives to prioritise growth over quality, combined with governance structures where decision-making authority may not rest with qualified accountants. For firms considering PE investment or acquisition, both the Raad and the AFM will scrutinise the arrangement.

Where CSRD fits for mid-tier firms

CSRD adds a new dimension to the mid-tier market. As of March 2026, the Netherlands has still not fully transposed the CSRD. The implementation bill was submitted on 13 January 2025, with an amendment introduced on 10 June 2025 to incorporate EU Omnibus simplification changes. The EU ’Stop the Clock’ directive delays Wave 2 and Wave 3 reporting by two years. Large public interest entities must report under ESRS for financial year 2024 onwards, and their sustainability statements require limited assurance.

For reguliere vergunninghouders, the CSRD creates both opportunity and risk. On one hand, large non-PIE entities coming into CSRD scope from 2025 onwards will need sustainability assurance, and not all will seek this from their current Big 4 auditor. On the other hand, performing sustainability assurance requires competencies that most mid-tier firms have not yet built. The NBA published Practice Note 1137 (revised) addressing corruption risks from an audit perspective, and Eumedion’s 2025 audit firm letter explicitly called on external auditors to dedicate particular attention to the double materiality assessment. Firms that position early for CSRD assurance work in the non-PIE segment may capture a growing market. Firms that take on sustainability assurance without adequate expertise will face regulatory scrutiny from the AFM.

Practical checklist for understanding your firm’s regulatory position

1. Confirm which supervisory bodies have jurisdiction over your firm: AFM (if Wta-licensed for statutory audits), NBA Raad voor Toezicht (for all other assurance and compilation work), or both. Map each engagement type to its supervising body.
2. Check your SRA membership status and what practical support you’re using. If you’re among the 46% of non-PIE firms not using SRA professional practice support, evaluate whether your internal quality infrastructure is sufficient on its own.
3. Review the AFM’s Sector in Beeld 2025 report for your firm’s size category. The AFM segments data into large, medium, and small reguliere vergunninghouders. Know where your firm sits and how your metrics (fraud risk identification rates, consultation frequency, data-driven audit rates, incident reporting) compare.
4. Assess whether the raised statutory audit thresholds (€7.5M assets, €15M turnover) have affected your audit client portfolio. Companies that previously required a statutory audit may now fall below the threshold. This affects both revenue and the firm’s risk profile.
5. If your firm has received or is considering private equity investment, review the Raad voor Toezicht’s 2024 comments on PE involvement and prepare documentation of voting rights and governance structures before the next monitoring questionnaire.

Common mistakes

• Assuming that AFM supervision and NBA review cover the same ground. The AFM’s Sector in Beeld 2025 report noted that the consultation rate at non-PIE firms (32% of audits) exceeds that at PIE firms (25%), yet quality review pass rates and AFM thematic findings suggest this higher consultation rate does not always translate into better file quality.
• Treating the SRA’s role as regulatory when it is not. The SRA provides support and represents member interests, but it does not set standards or grant licences. When SRA guidelines conflict with NVKS or Wta requirements, the regulatory standard prevails.

Related content

• Glossary: Reguliere vergunninghouder. Explains the AFM licence category for non-PIE audit firms and how it differs from an OOB licence.
• Financial Ratio Calculator. Useful for mid-tier firms performing ISA 520 analytical procedures on their expanding statutory audit portfolios.
• NBA quality review: preparation guide. The companion post covering how to prepare for the Raad voor Toezicht’s toetsing cycle.

Related tools and reading

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Frequently asked questions

Further reading and source references

• AFM Sector in Beeld 2025: Full data on the Dutch statutory audit market including non-PIE firm metrics, market share trends, and supervisory findings.
• Raad voor Toezicht Annual Report 2024: NBA quality review pass rates, recurring deficiencies, and private equity commentary.
• Wijzigingswet accountancysector: Legislative reform bill introducing AQIs and stricter governance for audit firms.
• NBA Quality Review: Preparation Guide: Companion post on preparing for the Raad voor Toezicht's toetsing cycle.