Definition:Occurrence basis
📋 Occurrence basis is a policy trigger mechanism under which a liability insurance policy responds to losses arising from events that take place during the policy period, regardless of when the resulting claim is actually reported to the insurer. This stands in contrast to a claims-made trigger, where coverage depends on when the claim is first made or reported rather than when the underlying event occurred. Occurrence-based policies are widely used in general liability, property, and motor insurance across virtually all major markets, though the relative prevalence of occurrence versus claims-made structures varies by line of business and jurisdiction.
⚙️ Under an occurrence-based policy, if a covered incident — such as a slip-and-fall injury on commercial premises — happens on March 15 of a given policy year, the policy in force on that date responds even if the injured party does not file a lawsuit until two or three years later. This creates what insurers call a "long tail" of potential reserve liability, because the carrier must estimate and set aside funds for claims that may not surface for years after the policy expires. Actuaries play a critical role in projecting these incurred but not reported liabilities, and the accounting treatment differs across regimes: US GAAP, IFRS 17, and local statutory frameworks each impose distinct reserving and discounting requirements on these long-tail obligations. For reinsurers, the occurrence trigger also defines how losses attach to treaty or facultative contracts, making the precise dating of occurrences a frequent source of contractual dispute.
💡 The choice between occurrence and claims-made coverage has far-reaching implications for both policyholders and carriers. Policyholders benefit from occurrence-based coverage because it eliminates gaps that can arise when switching insurers or when a policy lapses — the original policy remains responsible for events during its term indefinitely, subject to statutes of limitation. However, this open-ended exposure makes occurrence policies more expensive to price and more capital-intensive for insurers to support, which is why certain long-tail lines such as professional liability and directors and officers liability have largely migrated to claims-made forms. Understanding which trigger applies is essential during placement and claims handling, since misidentifying the trigger can lead to coverage denials, litigation, and significant financial consequences for all parties involved.
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