Business interruption (BI) insurance claims are calculated by measuring the financial loss a business suffers when it cannot trade normally — not the cost of repairing physical damage, but the profit it would have earned had the interruption never happened. Getting this figure right is the central dispute in most BI claims.
What Is the Indemnity Period and Why Does It Define Everything?
The indemnity period is the maximum time during which your insurer will pay for lost profit. It runs from the date of the insured event and is capped at whatever period your policy specifies — commonly 12, 24 or 36 months. If your policy says 12 months, your recoverable loss stops there regardless of how long actual recovery takes.
Forensic accountants start every BI calculation here because the indemnity period creates the boundaries. A business that underestimates its recovery time at policy inception and buys a 12-month indemnity period will find, post-loss, that its 18-month recovery falls partly outside cover. This is one of the most common and costly mistakes in BI insurance.
The period does not run from when you submit your claim. It runs from the date of the event — fire, flood, cyber attack, supplier failure — that triggered the loss.
How Do Insurers Calculate Gross Profit Under a BI Policy?
BI policies use a specific definition of "gross profit" that differs from the accounting definition most business owners know. In most UK policies, gross profit for BI purposes means turnover minus uninsured working expenses — costs that naturally fall away when the business is not trading, such as cost of raw materials or cost of goods sold.
Fixed costs — wages, rent, loan repayments, utilities on a fixed contract — generally continue regardless of whether the business is trading. These are the costs BI insurance is designed to cover. Variable costs that genuinely cease are deducted from turnover to arrive at the insured gross profit figure.
According to figures from the Association of British Insurers, disputes over the definition and calculation of gross profit account for a significant proportion of contested BI claims in the UK. The exact wording of your policy matters enormously — "gross profit" in one policy may be calculated quite differently from "gross profit" in another.
What Is a Trend Adjustment and When Does It Apply?
Insurers do not simply look at what turnover you had in the 12 months before the loss and extrapolate forward. They apply a trend adjustment — an upward or downward modification to the historical figures to reflect what the business would have achieved had the interruption not occurred.
If your business was growing at 15% per year before the loss, the insurer should trend the base period figures upward. If your sector was contracting, the adjustment may go the other way. The trend calculation requires evidence: management accounts, industry data, order books, marketing spend, and signed contracts are all relevant.
This is where significant money can be lost. An insurer that applies a conservative trend or fails to apply one at all will understate the loss. A forensic accountant working for the insured will assemble the evidence to support a well-founded trend adjustment.
What Additional Increased Cost of Working Can You Claim?
Most BI policies cover increased costs of working (ICOW) — the extra expenditure a business incurs to maintain normal operations during the interruption. If you rent temporary premises, run emergency logistics, pay overtime to recover lost production, or hire specialist equipment, these costs are recoverable.
There is a cap: the ICOW must be economic, meaning the cost must be no greater than the BI loss it prevents. If spending £50,000 on temporary premises saves £120,000 of gross profit loss, it is economic and recoverable. Businesses often fail to document ICOW properly during the crisis itself. Forensic accountants working on BI claims will work backwards from available records to reconstruct and justify these costs.
How a Forensic Accountant Builds the Claim Quantum
Quantifying a BI claim is a structured process. A forensic accountant will typically:
- Establish the indemnity period and its start date precisely
- Reconstruct the likely trading results for the period of interruption by reference to pre-loss accounts, management information and market conditions
- Apply trend adjustments supported by documented evidence
- Calculate the gross profit loss using the policy definition — not the statutory accounts definition
- Identify and quantify all recoverable ICOW and deduct genuine savings
- Produce a report that withstands scrutiny from the insurer's own loss adjusters and, if necessary, the courts
Where the insured and insurer cannot agree on quantum, the dispute typically goes to arbitration or litigation, at which point the forensic accountant may also act as an expert witness, presenting and defending the calculation before the tribunal.
Common Errors That Reduce Business Interruption Settlements
Several patterns consistently lead to businesses settling for less than they are entitled to. Using the wrong gross profit definition — the statutory accounts figure rather than the insured gross profit — is the most frequent error. Failing to trend historical results for known growth trajectories is the second. Not tracking increased costs of working in real time during the interruption is the third.
The fourth, and most damaging, is accepting the insurer's loss adjuster's calculation without independent review. Loss adjusters work for the insurer. They are not obliged to maximise your settlement. An independent forensic accountant works solely in your interest and will often identify material differences in the quantum.
Key Ledgers provides forensic accounting support for business interruption claims across England and Wales, including quantum preparation, expert witness reports, and support through litigation or arbitration. If you have a BI claim or are defending one, contact us to discuss the figures.
Written by Bharat Varsani FCCA. Bharat is a Chartered Certified Accountant and CPR Part 35-qualified expert witness with extensive experience quantifying business interruption losses across insurance, litigation and arbitration contexts. He acts for policyholders, insurers and as a joint expert in High Court proceedings.
Sources: Association of British Insurers — UK Insurance Key Facts; FCA v Arch Insurance (Supreme Court 2021) — Business Interruption Insurance Test Case.