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Across 35 NZX-listed auditor-change events between 2017-04-04 and 2025-05-15, the median share-price excess return versus the NZX Top 50 (FNZ ETF proxy) was -15.9% over the six months after the change and -26.6% over the twelve months after the change. 79% of events showed negative 12-month excess return. Data source: public.audit_changes table, forward returns computed from public.stock_prices.
An event study of share-price performance following auditor changes at NZX-listed issuers. Auditor rotations may indicate a range of situations — mandatory rotation, fee pressure, scope disagreements, or governance-led changes — and the data shown here is aggregate-only. Individual cases are data points, not incidents.
Event identification. We pull all rows from thepublic.audit_changes table where both old_auditor and new_auditor are populated — this excludes initial appointments (no predecessor) and standalone resignations (no successor). Events are extracted from NZX AUDITORS announcements.
Event date. We use effective_date when available, otherwise announcement_date. For each event we take the first available adjusted close within 10 calendar days at or after the event date as P₀.
Forward returns.6-month and 12-month holding-period total returns are computed from adjusted close (dividend-adjusted when available) using the same 10-day look-forward rule. Excess return equals the issuer's return minus the NZX Top 50 return over the identical window, using the Smartshares NZ Top 50 ETF (ticker FNZ) as a practical index proxy.
Filter. Events without at least 12 months of forward price data are included in the 6-month summary only. The methodology cutoff date is today (29 Jun 2026); 12-month readings require event dates on or before 29 Jun 2025.
Each row is an individual data point. Reasons given are the issuer's own stated rationale where disclosed in the NZX announcement.
Every switch is categorised by whether the outgoing and incoming auditor belong to the four largest global audit networks ("large-tier") or mid-tier/domestic firms. This is a descriptive classification of firm size and scope — not a quality ranking. Aggregate only; individual events are not attributed here.
| Direction | N | 12mo median excess vs FNZ | % below benchmark (12mo) |
|---|---|---|---|
| Large-tier → Large-tier | 17 | -0.3% | 100% |
| Large-tier → Mid-tier/Domestic | 7 | -0.4% | 100% |
| Mid-tier/Domestic → Large-tier | 2 | -0.4% | 100% |
| Mid-tier/Domestic → Mid-tier/Domestic | 9 | +0.1% | 40% |
Read carefully. This data describes what happened on average after switches of each type — it does not say which type of switch causes underperformance, and it says nothing about the quality of any specific auditor or any specific company.
Median 12-month excess return after an auditor change, grouped by GICS sector. Small-N cells should be interpreted cautiously.
| Sector | Events (N) | Median 12mo excess |
|---|---|---|
| Financials | 3 | -27.0% |
| Industrials | 3 | -8.8% |
| Consumer Staples | 3 | -47.4% |
| Information Technology | 2 | -13.0% |
| Healthcare | 2 | -9.7% |
| Energy | 1 | -83.9% |
Data sourced from publicly available NZX filings and annual reports. Our datasets may not be complete. Automated analysis can produce errors. Scores are calculated using disclosed methodology and are analytical tools, not investment ratings or recommendations. If you believe any data on this page is incorrect, please contact us at hello@nzxplorer.co.nz. For informational purposes only. Not investment advice.
Audit opinion types, going concern flags, and key audit matters
Audit firm market share, fee trends, and switching patterns
NZX audit market concentration, auditor tenure, fee trends, non-audit service ratios, and director-auditor independence cross-references for governance transparency.
| — |
| -34.5% |
| — |
| — |
| — |
| 19 Mar 2025 | Grant Thornton | Baker Tilly Staples Rodway | Auditor rotation after working with the same auditors since the Company was listed in 2004 | +14.1% | — | — | — |
| 07 Mar 2025 | KPMG | PwC | Good governance and length of tenure | -13.7% | +8.0% | -21.6% | -22.8% |
| 09 Sept 2024 | Deloitte | Grant Thornton | — | -10.2% | +1.0% | -11.2% | -26.2% |
| 02 Jul 2024 | EY | PwC | Good governance practice to change auditor after long period as external auditor | -6.1% | — | — | — |
| 01 Jul 2024 | PwC | EY | — | +14.1% | — | — | — |
| 10 Apr 2024 | KPMG | PwC | KPMG identified a conflict of interest after Downer's announcement on 4 March 2024 | 0.0% | — | — | — |
| 01 Apr 2024 | Deloitte | PwC | Mandatory auditor rotation in accordance with External Auditor Independence Policy requiring tender and formal assessment at least every 10 years | -4.0% | — | — | — |
| 02 Feb 2024 | Baker Tilly Staples Rodway | Deloitte | — | -31.4% | — | — | — |
| 09 Jan 2024 | KPMG | UHY Haines Norton | Cost savings objectives | -20.0% | — | — | — |
| 29 Aug 2023 | PwC | Grant Thornton | Mandatory rotation after 15 years as a matter of corporate governance | +10.5% | — | — | — |
| 28 Aug 2023 | PwC | EY | Good governance practice to change auditor after long period of service | -23.7% | — | — | — |
| 17 Jul 2023 | EY | UHY Haines Norton | Cost reduction and audit fee review | +11.1% | — | — | — |
| 30 Jun 2023 | RSM | UHY Haines Norton | — | -10.9% | — | — | — |
| 01 Apr 2023 | PwC | Deloitte | — | -3.4% | — | — | — |
| 07 Sept 2022 | Baker Tilly Staples Rodway | Grant Thornton | — | +54.5% | — | — | — |
| 31 Mar 2022 | KPMG | RSM | Cost reduction and benchmarking of audit fees against similar organisations | -10.1% | — | — | — |
| 06 Dec 2021 | PwC | KPMG | — | -19.2% | — | — | — |
| 01 Jul 2021 | EY | Deloitte | — | — | — | — | — |
| 01 Jul 2021 | KPMG | Deloitte | Mandatory rotation after 18 years of service | -4.5% | — | — | — |
Sample sizes per bucket are small (range 2–17 events). Interpret the patterns as directional observations that may warrant further investigation, not as predictive signals. Auditor switches can occur for many reasons including mandatory partner rotation, tenure limits, fee negotiations, scope changes, capability mismatches, and unrelated corporate events. The return data cannot separate these.
