Business Interruption Insurance Claims: A

Business interruption insurance claims require forensic accounting to establish the true loss. Insurers typically understate losses by 20-40%. Learn how claims are quantified and settled.

A business interruption insurance claim compensates a business for lost gross profit or revenue during an indemnity period following an insured event. Indemnity periods are typically 12, 18, or 24 months. In disputed claims, forensic accountants find that insurers understate the true loss by 20 to 40 percent. Quantifying the correct figure requires a counterfactual model comparing actual post-event performance against projected performance.

Last updated: 19 May 2026

Business Interruption Insurance Claims: A Forensic Accountant's Complete Guide

What Does Business Interruption Insurance Actually Cover?
What We See in Practice: Findings from 150+ Forensic Instructions
How Is a Business Interruption Loss Calculated?
What Is the "But For" Test and Why Does It Matter?
What Adjustments Are Applied to a Business Interruption Claim?
What Is the Role of the Forensic Accountant in a BI Claim?
How Long Does a Business Interruption Claim Take to Settle?
What Are the Most Common Reasons BI Claims Are Disputed?
What Is the FCA Test Case and How Does It Affect My Claim?
How Do I Instruct a Forensic Accountant for a BI Claim?

What Does Business Interruption Insurance Actually Cover?

Business interruption insurance covers the financial losses a business suffers when it cannot trade normally following an insured event such as fire, flood, theft, or a disease outbreak. The policy pays for lost gross profit or revenue for the duration of the indemnity period chosen at policy inception: typically 12, 18, or 24 months.

The key distinction between BI insurance and property insurance is this: property insurance repairs or replaces physical assets. BI insurance replaces the income stream those assets would have generated. A fire that destroys a restaurant kitchen may be settled quickly by property insurers for the cost of reinstatement. But the kitchen may take six months to rebuild, and during those six months the restaurant earns nothing. The BI policy covers that income gap.

BI policies typically cover the following heads of loss:

Loss of gross profit: the difference between turnover and variable costs that the business would have generated but for the insured event
Increased cost of working: additional expenditure incurred to minimise the interruption, such as temporary premises, equipment hire, or overtime payments
Additional increased cost of working: costs that are not strictly necessary to maintain output but are commercially reasonable
Payroll protection: some policies include a wages clause covering staff costs during the interruption period
Auditors' costs: the reasonable costs of quantifying the claim, including forensic accountant fees

What BI policies do not cover is equally important. They do not cover losses that arise from causes not listed in the policy. They do not extend beyond the indemnity period. They do not compensate for underperformance that pre-dates the insured event. The exact scope is defined by policy wording, which varies substantially between insurers, and that wording is frequently contested in disputed claims.

Understanding exactly what your policy covers before an insured event occurs is the most effective form of BI claim preparation. After the event, policy interpretation becomes an adversarial exercise.

What We See in Practice: Findings from 150+ Forensic Instructions

Across more than 150 forensic accounting instructions, including business interruption claims for retail, hospitality, professional services, and manufacturing businesses across England and Wales, consistent patterns emerge in how insurers approach the quantification of BI losses.

The most significant finding is this: in disputed claims, the insurer's initial quantification of the loss is typically 20 to 40 percent lower than the figure a forensic accountant establishes using the same underlying data. The gap is not usually the result of deliberate bad faith. It is the result of systematic methodology differences that consistently favour the insurer.

The variable cost deduction problem

The most common source of understatement is the over-deduction of variable costs when calculating gross profit. Insurers frequently classify costs as variable that a forensic accountant would classify as fixed or semi-fixed. For a hospitality business with a 70 percent gross margin, a dispute over cost classification that shifts 10 percent of turnover from gross profit to variable costs reduces the claim by a material sum. On a hospitality claim with a turnover of £800,000, that single methodology difference can move the claim quantum by £80,000 or more.

The comparison period argument

Insurers frequently argue for a comparison period that produces a lower loss figure. Where a business experienced unusual performance in the 12 months immediately prior to the insured event (a particularly strong year, a one-off contract, a significant marketing campaign), the insurer may argue for a longer historical average that dilutes the baseline. A forensic accountant challenges this by applying trend analysis and, where appropriate, special circumstances adjustments to ensure the comparison period is genuinely representative of the business's trajectory.

Mitigation arguments

Insurers routinely argue that the claimant failed to take reasonable steps to minimise the loss. In practice, most businesses do take mitigation steps, and many take steps that go beyond what is strictly required. The forensic accountant's role includes quantifying the value of mitigation steps actually taken, the cost of those steps, and the residual loss that remains after mitigation. When mitigation arguments are advanced without adequate quantification, they frequently overstate the mitigation credit the insurer is entitled to.

Quantum ranges from practice

Typical claim quantum ranges from instructions handled include: small retail or hospitality BI claims between £50,000 and £500,000; multi-site hospitality groups between £500,000 and £5 million; professional services firms between £100,000 and £2 million; and manufacturing or industrial businesses between £500,000 and £10 million or more. These ranges reflect the diversity of BI claims and illustrate why a forensic accountant's instruction is commercially justified even at the lower end of those ranges.

How Is a Business Interruption Loss Calculated?

A business interruption loss is calculated by comparing what the business actually earned during the indemnity period against what it would have earned had the insured event not occurred. The projected performance figure is the counterfactual, and establishing it correctly is the central technical challenge of every BI claim.

The standard methodology proceeds in the following steps:

Establish the historical baseline: typically, the three financial years immediately prior to the insured event are used. The most recent year is weighted most heavily because it is the most representative of the business's current trajectory.
Apply trend adjustments: if the business was growing or declining prior to the event, the historical baseline is adjusted to reflect that trend. A business that grew turnover by 15 percent per year for three years would not have a counterfactual equal to its prior year figure.
Apply special circumstances adjustments: where the historical data is not representative due to unusual prior-year events (a one-off contract, a temporary closure, a pandemic), special circumstances adjustments are applied to produce a more realistic baseline.
Calculate gross profit or revenue: the counterfactual revenue figure is translated into a gross profit figure by applying the business's gross margin. The gross margin used must reflect the trading conditions that would have prevailed during the indemnity period, not simply the historical margin.
Deduct actual performance: actual gross profit or revenue earned during the indemnity period is deducted from the counterfactual to produce the gross profit loss figure.
Add increased cost of working: additional costs legitimately incurred in minimising the interruption are added to the gross profit loss, subject to the economic limit clause in the policy.
Apply savings: costs saved as a direct result of the interruption (reduced variable costs, furlough wage savings, deferred marketing expenditure) are deducted where required by the policy wording.

The output is a net loss figure representing the total financial impact of the insured event on the business. In complex claims, this calculation produces a schedule of loss that runs to multiple pages and is supported by an expert forensic accountant's report prepared under CPR Part 35 standards.

For a detailed examination of the counterfactual methodology specifically, see our article on what is a counterfactual model in a business interruption claim.

What Is the "But For" Test and Why Does It Matter?

The "but for" test asks a single question: what would this business have earned but for the insured event? It is the legal and methodological foundation of every business interruption insurance claim, and it determines both the baseline revenue figure and the extent to which post-event trading results can be attributed to the insured event.

The "but for" test originated in tort law as the standard test of factual causation. It was adopted into insurance claims quantification because it provides a clear, binary framework: the insured event either caused a loss that would not otherwise have occurred, or it did not. Any loss that would have occurred regardless of the insured event is not covered by the BI policy.

In practice, applying the "but for" test to a BI claim is rarely simple. The central difficulty is that the post-event world is real, measurable, and observable, but the "but for" world (what would have happened without the event) is hypothetical and must be constructed from evidence. This is where the forensic accountant's expertise is essential.

Common disputes over the "but for" test

Insurers frequently argue that some or all of the post-event loss would have occurred regardless of the insured event, citing:

Pre-existing trends in decline (falling turnover before the event)
Market-wide downturns that affected all competitors equally
Management decisions made after the event that contributed to the loss
Structural changes in the market that would have reduced performance anyway

Each of these arguments requires forensic examination of the evidence. A pre-existing trend must be quantified and distinguished from the event-caused loss. A market-wide downturn must be evidenced by comparable business data. Management decisions must be evaluated against the standard of reasonableness in the circumstances. The forensic accountant responds to each insurer argument with quantified, evidenced analysis.

The Manchester Building Society v Grant Thornton [2021] UKSC 20 decision clarified the scope of duty test in professional negligence, reinforcing the principle that the scope of any professional duty must be carefully defined before loss is attributed to a breach. While this case addresses professional negligence rather than BI claims directly, its reasoning is applied in expert witness reports addressing the scope of the forensic accountant's counterfactual model.

What Adjustments Are Applied to a Business Interruption Claim?

Several categories of adjustment are applied to a BI claim calculation to move from a raw historical baseline to a properly calibrated loss figure. Understanding each adjustment and the direction in which it moves the claim is essential for both claimants and their advisers.

Adjustment type	Direction	When it applies
Trend adjustment (growth)	Increases claim	Business was growing at a consistent rate pre-event
Trend adjustment (decline)	Decreases claim	Business was declining pre-event; insurer argues this
Special circumstances (new business)	Increases claim	Business had insufficient trading history; projected forward from business plan
Special circumstances (prior unusual event)	Bidirectional	Prior year included a one-off contract or temporary closure
Seasonal adjustment	Bidirectional	Business is highly seasonal; insured event occurred in peak or off-peak period
Increased cost of working	Increases claim	Additional costs incurred to maintain or restore output
Savings	Decreases claim	Variable costs saved during interruption period
Underinsurance	Decreases claim	Policy sum insured is lower than the actual gross profit at risk

The trend adjustment is the most frequently contested adjustment in practice. Insurers typically advocate for a simple three-year average with no trend applied, while the forensic accountant analyses the actual trajectory of revenue growth, gross margin development, and any identifiable catalysts (new contracts, market share gains, price increases) to construct the most accurate counterfactual baseline.

Underinsurance is a particularly important adjustment because it applies a proportional reduction to the entire claim. If a business insures gross profit of £500,000 when its actual gross profit at risk is £1,000,000, the insurer will apply a 50 percent reduction to every head of loss. Many businesses are significantly underinsured because they have not reviewed their gross profit figure at renewal, or because the policy uses a definition of gross profit that differs from the accounting definition.

For businesses undergoing a business interruption claim, the forensic accounting service for business interruption claims at Key Ledgers covers quantification, expert reporting, and mediation support.

What Is the Role of the Forensic Accountant in a BI Claim?

The forensic accountant's role in a business interruption claim is to provide an independent, evidence-based quantification of the financial loss caused by the insured event. This role is distinct from the claimant's accountant, whose primary obligation is to the client, and from the insurer's accountant, whose role is to scrutinise the claim on the insurer's behalf.

Where a forensic accountant is instructed as a single joint expert, they prepare one report for both parties under CPR Part 35. Where claims are contested and the parties cannot agree a joint expert, each party instructs their own expert, and the two experts may be required to produce a joint statement identifying points of agreement and disagreement.

The specific tasks a forensic accountant carries out in a BI claim include:

Reviewing the policy wording to identify the applicable heads of loss and any limiting clauses
Analysing the claimant's financial records (management accounts, VAT returns, payroll records, sales data) to establish the historical baseline
Constructing the counterfactual model, including all applicable adjustments
Calculating the gross profit loss for each period of the indemnity period
Quantifying the increased cost of working claims and testing them against the economic limit clause
Preparing a detailed schedule of loss in a format suitable for negotiation and, if required, expert evidence at arbitration or trial
Responding to the insurer's forensic accountant's counter-report, identifying the basis of any discrepancies

The forensic accountant owes their primary duty to the court or arbitrator, not to the instructing party. This is a critical point: a well-prepared CPR Part 35 expert report carries significant weight precisely because the expert's independence is explicit and enforceable. Expert reports that shade the analysis towards the instructing party's position are exposed in cross-examination and carry reduced weight.

Key Ledgers' forensic accountant expert witness services cover business interruption, professional negligence, and commercial dispute instructions across England and Wales.

How Long Does a Business Interruption Claim Take to Settle?

An uncontested business interruption claim typically settles within 12 to 18 months of the insured event. A disputed claim that proceeds to mediation or arbitration typically takes 3 to 5 years. The timeline depends on the complexity of the loss, whether the parties can agree on methodology, and the insurer's conduct in handling the claim.

Key milestones in the BI claim timeline are:

Month 0: Insured event occurs
Month 1: Notification to insurer (most policies require notification within 30 days)
Month 3 to 6: Interim payment request submitted; interim forensic accountant instruction
Month 4 to 8: Forensic accountant instruction finalised; data gathering and analysis begins
Month 9 to 12: Expert report produced; claim formally submitted
Month 12 to 18: Insurer's forensic accountant reviews claim; counter-report produced
Month 12 to 24: Negotiation or mediation; settlement or referral to arbitration
Year 3 to 5: Arbitration or litigation (contested claims only)

Interim payments are an important tool for businesses whose cashflow is severely impacted by the interruption. Most BI policies allow the claimant to request an interim payment based on an undisputed portion of the loss. The forensic accountant can prepare a schedule of the undisputed minimum loss to support an interim payment request. Receiving interim funds while the full claim is negotiated can be commercially critical for a business that is still trading at reduced capacity.

For a detailed timeline analysis, see our article on how long business interruption claims take to settle.

What Are the Most Common Reasons BI Claims Are Disputed?

Business interruption claims are disputed on several recurring grounds. Knowing these in advance allows claimants and their advisers to gather the evidence needed to address each argument before the insurer raises it.

The most frequent grounds for dispute are:

Policy wording disputes: whether the trigger event is actually covered by the policy (the FCA Test Case resolved many disease and prevention of access disputes, but policy wording variations continue to generate new disputes)
Methodology disputes: whether the counterfactual model uses the correct historical period, whether trend adjustments have been correctly applied, and whether the gross profit definition used in the policy matches the one used in the calculation
Variable cost disputes: which costs should be treated as variable (and therefore deducted from turnover to arrive at gross profit) and which should be treated as fixed
Mitigation disputes: whether the claimant took all reasonable steps to reduce the loss, and what credit the insurer is entitled to for mitigation already achieved
Underinsurance disputes: whether the policy sum insured was adequate at the time of the event
Causation disputes: whether the insured event caused all or only part of the loss, particularly where there is a pre-existing trend or a concurrent uninsured cause

The single most effective step a claimant can take to shorten the dispute resolution process is to instruct a forensic accountant early, before submitting the claim. An expert-prepared claim with a clear, well-reasoned methodology is much harder for an insurer to contest than a claim prepared by the business or its general accountant without reference to the applicable forensic accounting standards.

What Is the FCA Test Case and How Does It Affect My Claim?

The FCA Test Case, formally FCA v Arch Insurance (UK) Ltd and others [2021] UKSC 1, was a Supreme Court decision that required insurers to pay business interruption claims under disease clauses and prevention of access clauses that they had previously been refusing to pay. The case arose from widespread insurer denials of Covid-19 BI claims and was brought by the Financial Conduct Authority on behalf of policyholders.

The Supreme Court found, in January 2021, that insurers were required to pay claims under policies with disease clauses covering notifiable diseases and under policies with prevention of access clauses covering government-imposed restrictions. The decision affected around 370,000 policyholders in the UK and resulted in total insurer payments estimated at several billion pounds.

The FCA Test Case has several ongoing implications:

It established that disease and prevention of access clauses must be interpreted broadly in favour of policyholders where the policy wording is ambiguous
It confirmed that the counterfactual loss calculation must reflect what the business would have earned in the absence of the entire pandemic, not just in the absence of local restrictions
It resolved methodological disputes about trend adjustments in the context of market-wide downturns caused by the insured event itself
It set a precedent for the approach courts and arbitrators will take to similar disputes involving disease clauses in future policies

For businesses with outstanding Covid-19 BI claims that were not settled following the FCA Test Case, there remain grounds to revisit those claims, particularly where the original settlement was reached without independent forensic accounting input. Several insurers settled claims on a basis that did not fully reflect the quantum established by the Supreme Court's guidance on trend adjustments and the scope of the insured event.

How Do I Instruct a Forensic Accountant for a BI Claim?

Instructing a forensic accountant for a business interruption claim follows a structured process. The earlier the instruction is made, the more effectively the forensic accountant can shape the approach to gathering and preserving financial evidence.

Identify the need for instruction: any BI claim where the insurer has raised a methodology dispute, produced a counter-quantification, or is taking more than 90 days to accept or reject the claim should be referred to a forensic accountant.
Gather initial documents: the forensic accountant will require the policy schedule and wording, at least three years of financial statements, management accounts and VAT returns for the interruption period, sales records or booking data if available, and any correspondence with the insurer to date.
Agree the scope of instruction: the instruction may be as a claimant's expert (producing a report for your own use), as a single joint expert (agreed between both parties), or as a CPR Part 35 expert witness (if proceedings have been issued or are contemplated).
Receive the report: the forensic accountant produces a written report setting out the methodology, the data used, the adjustments applied, and the resulting loss figure, with supporting schedules. The report is written to withstand cross-examination.
Use the report in negotiations: the report forms the basis of the claim submission or, in a disputed claim, the expert evidence submitted to mediation, arbitration, or court.

CPR Part 35 compliance is mandatory for expert reports used in court proceedings, but a report prepared to CPR Part 35 standards carries greater evidential weight in pre-litigation negotiations as well. Insurers and their advisers take CPR-compliant expert reports more seriously than accountant reports not prepared to that standard.

Frequently Asked Questions: Business Interruption Insurance Claims

What is the indemnity period in a business interruption policy?

The indemnity period is the maximum duration for which the policy will pay a business interruption loss. It begins on the date of the insured event and typically runs for 12, 18, or 24 months depending on the period selected at policy inception. Once the indemnity period expires, no further loss is recoverable under the policy regardless of whether the business has fully recovered.

Can I claim for increased cost of working under my BI policy?

Yes, most business interruption policies include an increased cost of working (ICOW) clause. This covers additional expenditure incurred to limit the interruption: temporary premises rental, equipment hire, overtime wages, and expedited delivery costs. ICOW payments are subject to an economic limit, meaning the additional cost cannot exceed the gross profit loss it prevents.

What is the difference between gross profit and net profit in a BI claim?

Most BI policies use a definition of gross profit that is different from the accounting definition. The policy gross profit is typically turnover minus uninsured working expenses (variable costs). Fixed costs such as rent, salaries, and loan repayments continue during the interruption and are therefore covered. Net profit, which deducts all costs, is not the correct measure for most BI claims.

What happens if I am underinsured on my business interruption policy?

If the sum insured is lower than the actual gross profit at risk during the indemnity period, the insurer applies an average (proportional reduction) to the entire claim. For example, if gross profit at risk is £1,000,000 but the sum insured is £600,000, the insurer pays 60 percent of every head of loss. Underinsurance is common and is one of the first checks a forensic accountant carries out.

Does my BI policy cover losses from a pandemic or disease outbreak?

This depends on the specific policy wording. Following the FCA Test Case [2021] UKSC 1, policies with disease clauses covering notifiable diseases, and policies with prevention of access clauses, were required to pay Covid-19 claims. Policies without such clauses generally did not provide cover. For future disease events, cover depends on whether the triggering disease qualifies under the policy's specific disease clause wording.

Can I recover the cost of a forensic accountant under my BI policy?

Many business interruption policies include a clause covering the reasonable professional fees incurred in preparing and substantiating the claim, including forensic accountant fees. This clause is often called the accountants' clause or professional fees clause. Check your policy schedule. Even where fees are not covered under the policy, the cost of a forensic accountant is typically justified by the increased claim quantum achieved.

What is the role of the forensic accountant as a CPR Part 35 expert witness?

A CPR Part 35 expert witness owes their primary duty to the court, not to the party who instructs them. The forensic accountant prepares a report that is admissible as expert evidence in court or arbitration proceedings. The report must comply with CPR Part 35 requirements including a declaration of independence. This standard ensures the report carries maximum evidential weight and withstands cross-examination.

What documents does a forensic accountant need to quantify a BI claim?

A forensic accountant typically requires: the insurance policy schedule and wording; three years of statutory accounts; management accounts covering the interruption period; VAT returns for at least three years; payroll records; detailed sales or booking data; and any insurer correspondence or preliminary settlement offers. For hospitality businesses, till data, reservation records, and covers-per-day reports are particularly relevant.

Business interruption insurance claims require methodological precision to ensure the true loss is captured. The indemnity period, gross profit definition, counterfactual baseline, and applicable adjustments are all contested in most material claims. In disputed claims, forensic accountants find that initial insurer quantifications understate the loss by 20 to 40 percent. Early instruction of a CPR Part 35 forensic accountant is the most effective step a claimant can take to ensure the full loss is recovered within the shortest possible timeframe, which is typically 12 to 18 months for uncontested claims and 3 to 5 years for litigated disputes.

To instruct Bharat Varsani FCCA as your forensic accountant in a business interruption claim, contact Key Ledgers at our contact page.

About the author: Bharat Varsani FCCA is a forensic accountant and CPR Part 35 expert witness based in London, with over 150 instructions including business interruption insurance claims for hospitality, retail and professional services businesses across England and Wales.