An ad hoc audit is a one-time, narrowly focused examination commissioned to answer a specific question inside a business, such as whether a target company’s earnings hold up in due diligence, how much an employee embezzled, or whether grant funds were spent within their restrictions. The Latin phrase means “for this purpose,” and that captures what separates the work from the recurring annual audit: an ad hoc audit exists because something happened, and it stops once that something has been answered.
What Makes an Audit “Ad Hoc”
Three traits set these engagements apart. They are non-recurring; nobody schedules one for next quarter. The scope is deliberately narrow, confined to whatever triggered the work. And a specific party initiates it: a board, outside counsel, a regulator, a lender, or a potential buyer.
Most ad hoc audits are structured as agreed-upon procedures (AUP) engagements. The party commissioning the work and the auditor decide in advance which procedures the auditor will perform, what subject matter those procedures apply to, and how results will be reported. The auditor does not issue an opinion on the financial statements. The deliverable is a factual report listing what was done and what was found.
For public companies, the governing standard is the PCAOB’s AT Section 201, which requires auditor independence, agreement on procedures before fieldwork begins, and a report restricted to specified parties who accept responsibility for the sufficiency of those procedures.1Public Company Accounting Oversight Board. AT Section 201 – Agreed-Upon Procedures Engagements For private companies and nonprofits, the AICPA’s SSAE 19 applies. Under SSAE 19, auditors no longer need a written assertion from the responsible party, procedures can be developed as the engagement progresses, and report-use restrictions are optional rather than mandatory.2Association of International Certified Professional Accountants. AICPA Statement on Standards for Attestation Engagements No. 19 The optional restriction matters in practice: findings can be shared with insurers, regulators, or transaction counterparties when the practitioner leaves the report unrestricted.
When You Need One
Mergers, Acquisitions, and Divestitures
Due diligence is one of the most common triggers. A buyer usually wants a quality of earnings analysis rather than a full audit: normalize one-time events, verify revenue recognition, test working capital, and check whether reported expenses match actual operations. The question is forward-looking in a way a standard audit is not. Can the buyer trust the earnings stream that justifies the purchase price?
Suspected Fraud or Embezzlement
A whistleblower report, unusual account activity, or a tip from an employee can trigger a forensic ad hoc audit that traces specific transactions and quantifies the loss. These engagements require reconstructing how the scheme worked through internal control weaknesses, and they often need evidence preserved in a way that will hold up if the matter goes to court.
Litigation Support
Breach-of-contract disputes, insurance claims, and partnership dissolutions frequently need damages calculated with enough rigor to survive cross-examination. The auditor may reconstruct lost profits from historical sales data, analyze projected margins, or trace funds through multiple accounts. The work product becomes the foundation for expert testimony.
Targeted Compliance Reviews
Federally funded organizations face specific audit obligations. Any non-federal entity spending $1,000,000 or more in federal awards during a fiscal year must undergo a single audit under the Uniform Guidance. A single audit covers broad compliance, though. When a particular grant’s expenditure rules are in question, or when a lender wants to confirm compliance with a debt covenant, an ad hoc review targets that one obligation without the overhead of a full compliance audit. Federal agencies, inspectors general, and the GAO also retain authority to arrange additional audits beyond the single audit when circumstances warrant it.3eCFR. 2 CFR Part 200 Subpart F – Audit Requirements
How It Differs From a Standard Audit
A standard financial statement audit renders an opinion on whether the statements are presented fairly under Generally Accepted Accounting Principles. The auditor plans and performs the work to obtain reasonable assurance the statements are free from material misstatement.4Social Security Administration Office of the Inspector General. Independent Auditor’s Report on the Audit of Social Security Administration Fiscal Year 2013 Financial Statements An ad hoc audit answers a defined question instead. How much was stolen? Does this subsidiary’s revenue hold up under scrutiny? Were grant funds spent properly?
Frequency separates them as well. Every issuer with securities registered under the Securities Exchange Act must file an annual report containing audited financial statements.5eCFR. 17 CFR 240.13a-1 – Requirements of Annual Reports Ad hoc audits have no set schedule. They happen once, driven by a specific event, and may never happen again.
The applicable standards diverge, too. Standard audits follow Generally Accepted Auditing Standards. Ad hoc engagements typically operate under AUP standards, where the client defines the procedures and the auditor reports findings without an opinion.
How the Engagement Runs
Engagement Letter
Every ad hoc audit starts with a formal engagement letter that works as a contract. It specifies what the auditor will do, what subject matter is covered, what period is in play, and how the report will be formatted. It also confirms that no opinion on the financial statements will be issued. Getting this document right is critical because it controls the boundaries of the entire engagement: procedures not listed will generally not be performed, and findings outside the defined scope will not appear in the report.
Fieldwork
Data-gathering varies with the trigger. A compliance review might mean pulling invoices, verifying expenditure categories against grant requirements, and interviewing program managers. A forensic fraud investigation looks entirely different: the team analyzes journal entries for patterns, reconstructs bank account activity, examines electronic communications, and interviews employees with knowledge of the suspected scheme. When litigation is likely, auditors focus on establishing a chain of custody for evidence so nothing can be challenged as tampered with or incomplete.
Data analytics tools play a growing role. Software can flag abnormal transaction patterns, identify duplicate vendor payments, and detect round-dollar entries that suggest manual manipulation, letting a small team process thousands of transactions in the time manual review would take for a handful.
The Report
Once fieldwork ends, the auditors apply the agreed-upon procedures to the collected data and document factual findings. The report lists what was done and what was found, sometimes with detailed exhibits summarizing evidence.1Public Company Accounting Oversight Board. AT Section 201 – Agreed-Upon Procedures Engagements For a fraud engagement, that might mean a calculated loss amount tied to specific transactions. For a compliance review, a list of expenditures that did or did not meet grant requirements.
Choosing the Auditor and Protecting Privilege
Independence
Publicly traded companies cannot simply hand every ad hoc engagement to their existing external audit firm. SEC rules prohibit the external auditor from providing certain non-audit services to audit clients because those services impair independence. The prohibited list includes appraisal and valuation services, fairness opinions, internal audit outsourcing, actuarial services, and management functions.6U.S. Securities and Exchange Commission. Audit Committees and Auditor Independence A forensic investigation or valuation-related ad hoc audit may fall within those prohibitions, meaning a separate firm is required.
Even for private companies where SEC independence rules do not apply, using a different firm can be wise. If the ad hoc audit turns up problems with the annual financial statements, the auditor who signed the clean opinion should not be the one investigating whether the clean opinion was wrong.
Privilege
This is where companies make the most expensive mistakes. When an ad hoc audit involves potential fraud, regulatory violations, or anything that might lead to litigation, how the engagement is structured determines whether findings are protected by attorney-client privilege or discoverable by an opposing party.
Under the Kovel doctrine, courts have extended attorney-client privilege to communications between a client, their attorney, and a third-party expert when the expert is retained by the attorney to help provide legal advice. For the protection to hold, the expert must be working at the attorney’s direction, and the communications must be for the purpose of facilitating legal counsel rather than simply gathering facts. If instead the company’s management hires the forensic accountant directly without involving counsel, the resulting work product is generally not privileged and can be subpoenaed.
The practical takeaway: if there is any real chance the ad hoc audit could lead to litigation or regulatory action, have outside counsel retain the forensic firm. Make clear in the engagement letter that the expert is assisting counsel in providing legal advice. And understand that any report intended to be disclosed to third parties, such as the IRS or a regulator, loses its privilege protection the moment it leaves the attorney’s hands.
Cost and Timeline
Costs vary with complexity. Forensic accounting professionals generally bill between $300 and $400 per hour for investigative analysis, report preparation, consulting with counsel, and expert witness preparation. Court appearances and deposition testimony bill separately and often carry minimum appearance fees. Most engagements require a signed agreement and an upfront retainer applied against billed hours.
A straightforward compliance review with a defined record set and a narrow question might wrap in four to six weeks. Complex fraud investigations involving multiple entities, years of transactions, and potential litigation can stretch to several months or longer. The engagement letter should include a realistic scope estimate, though timelines shift when fieldwork reveals additional issues. Firms typically invoice monthly, and additional retainers may be requested as a case expands. Flat-fee packages exist for limited-scope work where record volume is predictable, such as a targeted financial review tied to a specific contract dispute. For anything open-ended, hourly billing is standard.
What the Findings Can Trigger
Internal Fixes
The most immediate use is to correct whatever prompted the audit. Findings may lead to changes in internal controls, termination of employees involved in misconduct, renegotiation of a purchase price based on adjusted earnings, or a decision to walk away from an acquisition. A quantified loss from a forensic engagement can also support an insurance claim under a fidelity bond or crime policy.
SEC Disclosure
For public companies, an ad hoc audit that reveals errors in previously issued financial statements can trigger mandatory disclosure. Under Item 4.02 of Form 8-K, if the board, audit committee, or authorized officers conclude that previously issued financial statements should no longer be relied upon because of an error, the company must file a Form 8-K within four business days.7Securities and Exchange Commission. Form 8-K The filing must identify the affected statements, describe the underlying facts, and state whether the matter was discussed with the independent auditor. If the independent auditor is the one advising non-reliance, parallel disclosures are required and the company must ask the auditor to submit a letter to the SEC confirming or disputing the company’s characterization.
Deducting a Theft Loss
When a forensic audit quantifies an embezzlement loss, the business may be able to claim a federal tax deduction. Under IRC Section 165, a theft loss is deductible in the year the taxpayer discovers it, provided the loss is not compensated by insurance and there is no reasonable prospect of recovery.8Office of the Law Revision Counsel. 26 USC 165 – Losses For businesses, the deduction is available for losses incurred in a trade or business or in a transaction entered into for profit. The loss must result from conduct classified as theft under applicable state law, which is why the forensic audit’s factual findings and evidence trail matter: they are the documentation the IRS will look for if the deduction is challenged.
Expert Testimony
If the engagement was commissioned to support litigation, findings must survive judicial scrutiny before reaching a jury. Federal Rule of Evidence 702 requires expert testimony to be based on sufficient facts, produced through reliable methods, and reliably applied to the facts of the case.9Legal Information Institute. Rule 702 – Testimony by Expert Witnesses Under the framework established in Daubert v. Merrell Dow Pharmaceuticals, the trial judge acts as gatekeeper on whether the methodology can be tested, has been subjected to peer review, has a known error rate, and enjoys general acceptance in the relevant professional community.10Legal Information Institute. Daubert v. Merrell Dow Pharmaceuticals, 509 U.S. 579 (1993) A forensic report built on sloppy methodology or conclusions that leap beyond the data can be excluded before the jury ever sees it. The engagement letter, the documented procedures, and the chain of custody all feed the admissibility analysis, which is why rigorous procedure during fieldwork pays off at trial.