Auditor Rotation as Protection: What Mandatory Rotation Achieves

Why long auditor relationships can be a risk

An auditor who has known a company for many years knows where the figures come from, who works reliably, and which items are delicate. That makes the auditor efficient. It can also make the auditor lenient. Anyone who meets the same people every year eventually checks the deviation from last year rather than the matter itself.

Lawmakers have therefore decided for large companies: after a certain period, the auditor must change. This article asks: Does mandatory auditor rotation actually protect against too much closeness, or does it cost more quality than it delivers? To answer it, we first clarify the rules, then present the thinking model of the rotation scale, look at the research with two readings, and finally apply the result to mid-sized businesses.

What external and internal rotation mean

Two forms are distinguished. In external rotation, the entire audit firm changes. In internal rotation, the firm stays, but the responsible audit partner, the person who signs the audit opinion, is replaced. After a change, a cooling-off period applies: the former auditor may not take the mandate back for a certain time.

Public-interest entities are mainly listed companies, banks, and insurers. For a medium-sized GmbH, the German limited liability company, that is subject to audit, there is no statutory maximum term. Who has to be audited at all is described in Statutory audits in mid-sized companies. The United States has chosen a different path: there the responsible partner rotates, and after a lengthy debate the audit regulator PCAOB did not introduce mandatory rotation of the firm (Friedrich, Pappert, and Quick 2023).

The thinking model: the rotation scale

The basic conflict is explained by principal-agent theory, which How independent are auditors? presents in detail: the auditor checks management on behalf of the owners but is chosen and paid by the company it audits. Rotation addresses one specific point of this relationship, namely time.

I describe the effect as the rotation scale. On one side lies the familiarity threat: with every year, personal closeness grows, as do the wish to keep the mandate and the tendency not to question one's own earlier judgments. On the other side lies the loss of knowledge: a new auditor does not yet know the client's business, systems, and risks and needs time to get up to speed. Rotation helps when the first pan weighs more than the second.

An everyday analogy: anyone who drives the same route to work for years knows every bend but easily overlooks the new sign. A passenger driving the route for the first time notices it immediately but takes a wrong turn somewhere else.

Rotation does not replace skepticism; it organizes the fresh look before it is needed.

What research shows: two readings

First reading: the change improves the audit

Friedrich, Pappert, and Quick (2023) examined 287 German public-interest entities over the years 2014 to 2019, the transition period before the EU rule took full effect. 103 of them changed auditors during this period. Audit quality was measured through so-called discretionary accruals, accruals that management can form at its own discretion and that lend themselves to earnings management. In the first year after the change, these discretionary accruals were lower and the audit took longer, which points to more effort by the new auditor.

The authors themselves name important limitations. The effect appeared only at smaller listed companies outside the most prominent stock market segment. For the prominent companies they found no difference in the first year; instead these paid lower fees after the change because auditors compete for such mandates. In the period before the EU rule, the effect did not appear. The authors interpret this to mean that new auditors in a market that expects rotation place particular weight on their reputation. A study from Vietnam with 170 listed companies also reaches a positive result but found low audit quality in the financial sector despite mandatory rotation (Nguyen, Nguyen, and Bui 2026).

Second reading: the change costs more than it delivers

Cheynel and Zhou (2024) reach the opposite result using a market model. According to their estimates, a longer tenure lowers the cost of an audit, raises quality, and reduces misstatements. Mandatory rotation would lead to considerably more changes, even before the maximum term expires, and new auditors would initially deliver lower quality. Overall, misstatements would become more frequent. A survey of 235 auditors in Indonesia shows that the view also depends on one's position: small firms supported rotation, while the large firms considered it less necessary because of partner rotation and internal quality control (Fitriany and co-authors 2025).

I consider the first reading more robust because it rests on observed changes in Germany, whereas the second builds on a model using US data. But the findings also show that rotation is no cure-all. It works where audit quality was not already high, and it works most strongly in the first year.

What a documented case shows about long mandates

The tightening through the FISG was a response to the collapse of the payment services company Wirecard in June 2020. According to public reports, the same audit firm had audited the financial statements from 2009 to 2018. During this time, according to the case study by Bloch, Hunter, and Kleinman (2025), five different audit partners signed, so internal rotation did take place. For 2019 the audit opinion was withheld because sufficient evidence was missing for trust balances of around 1.9 billion euros. The sequence is described in Chronicle of an Accounting Scandal.

The case does not prove that the long tenure was the cause. But it shows two things. First, changing the person does not necessarily protect against a habit of the firm. Second, the decisive fresh look came from outside, through a special investigation by another firm. The criminal proceedings have not been concluded; the presumption of innocence applies to everyone involved. How a few large firms shape the market and thus make changes harder is described in The Big Four.

How to use the principle in your own business

A small business does not have to change its tax adviser or auditor, and changing purely on principle would often be disproportionate. An adviser with ten years of experience in the business is an asset. But a lighter form can be derived from the rotation scale, which I call the fresh-look rule: the person does not change, but on a fixed schedule a third party looks at a selected area.

1. Select an area

   Each year, choose an area with a lot of judgment: inventory valuation, provisions, open receivables, accounting for work in progress.

2. Engage a third party

   Ask a second firm, an advisory board, or an experienced peer from your network to review this area. A limited engagement keeps costs low.

3. Disclose assumptions

   Have your adviser write down beforehand which assumptions the valuation rests on. The third party checks these assumptions, not only the result.

4. Discuss the result

   Discuss deviations with both. The point is not to find someone to blame but whether a habit still fits the situation.

If there are co-owners or an advisory board, they should select the area and engage the third party, not management. How such a body works is described in Advisory boards in mid-sized companies. The logic also applies to banks, insurance brokers, and IT providers: anyone who has been the same for years deserves an occasional comparison.

What follows beyond the individual case, and where the limits lie

Rotation is a tool against a structural problem: the relationship between auditor and audited company grows closer over time. It does not solve the basic problem that the auditor is paid by the audited party. That requires further building blocks such as limits on advisory work, effective supervision, and bodies that select the auditor. What such building blocks look like in a small business is described in Corporate governance for small businesses.

The limits of the findings are clear. The German study looks at the transition period, not the years under full application of the rule. Audit quality is measured indirectly through accounting ratios, not directly. There are practically no data on mid-sized companies. Whether a fresh look has the same effect in a small business is an extrapolation that I consider plausible but that has not been measured.

Conclusion: rotation protects when the change is a real fresh start

To the guiding question: mandatory rotation partly protects against too much closeness, but not everywhere and not without costs. German data show better audit quality in the first year after a change, especially at companies where quality was not already high. Models and experience from other countries are a reminder that knowledge is lost with every change. The rotation scale sums it up: rotation pays off when distance counts for more than familiarity.

For your business the conclusion is more practical: you do not have to replace anyone to get a fresh look. A limited, regular engagement of a third party brings the benefit of rotation almost without its costs.

• Note how long your tax adviser, auditor, and bank have worked for your business.
• Select one area with a lot of judgment for review by a third party.
• Ask your adviser to write down the assumptions for this area.
• Agree with co-owners or the advisory board on who commissions the fresh look.