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📊 '''IBNR reserve''' — short for ''incurred but not reported'' reserve — is an [[Definition:Actuarial | actuarial]] estimate that an [[Definition:Insurance carrier | insurer]] establishes to account for [[Definition:Claim | claims]] that have already occurred but have not yet been reported to the company, as well as for expected future development on claims that have been reported but whose ultimate cost is not yet fully known. It represents one of the most significant components of an insurer's overall [[Definition:Loss reserve | loss reserves]] and appears on the [[Definition:Balance sheet | balance sheet]] as a [[Definition:Liability | liability]], directly affecting reported [[Definition:Surplus | surplus]] and [[Definition:Underwriting result | underwriting results]]. Long-tail lines such as [[Definition:General liability insurance | general liability]], [[Definition:Workers' compensation insurance | workers' compensation]], and [[Definition:Professional liability insurance | professional liability]] tend to carry substantially larger IBNR reserves than short-tail lines like [[Definition:Auto insurance | auto physical damage]], because of the extended period between the occurrence of a loss event and its final settlement.

🔢 Actuaries estimate IBNR reserves using a range of methods — including [[Definition:Chain-ladder method | chain-ladder]] (link ratio), [[Definition:Bornhuetter-Ferguson method | Bornhuetter-Ferguson]], and [[Definition:Expected loss ratio method | expected loss ratio]] techniques — applied to [[Definition:Loss triangle | loss development triangles]] that track how [[Definition:Paid loss | paid]] and [[Definition:Incurred loss | incurred losses]] mature over successive evaluation periods. The selection among methods, the judgment applied to development factors, and the treatment of anomalies (such as a large individual claim distorting a development year) all introduce a degree of estimation uncertainty that actuaries communicate through ranges and confidence intervals. Management then selects a carried reserve point within these ranges, often incorporating its own views on emerging trends, legal environment changes, or [[Definition:Inflation | claims inflation]]. External [[Definition:Auditor | auditors]] and [[Definition:Insurance regulator | regulators]] review these estimates closely, and material deficiencies or redundancies in IBNR reserves can trigger [[Definition:Regulatory action | regulatory intervention]] or restatements of financial results.

⚠️ Accurate IBNR estimation is central to the financial integrity of any insurance operation. Understating IBNR inflates current-year [[Definition:Profit | profitability]] and [[Definition:Surplus | surplus]], potentially masking deteriorating [[Definition:Loss ratio (L/R) | loss ratios]] until the shortfall surfaces as [[Definition:Adverse development | adverse development]] in later periods — a pattern that has contributed to notable carrier insolvencies. Overstating IBNR, while more conservative, suppresses reported earnings and may impair an insurer's competitive position or lead to unnecessary [[Definition:Rate increase | rate increases]]. The transition to [[Definition:IFRS 17 | IFRS 17]] has introduced additional granularity to how insurers recognize and disclose reserve movements, including IBNR components. For [[Definition:Insurtech | insurtech]] firms and analytics vendors, improving the speed and precision of IBNR estimation — through [[Definition:Machine learning | machine learning]], real-time claims data ingestion, and automated [[Definition:Loss triangle | triangle]] analysis — represents one of the highest-value applications of technology in insurance finance.

'''Related concepts:'''
{{Div col|colwidth=20em}}
* [[Definition:Loss reserve]]
* [[Definition:Chain-ladder method]]
* [[Definition:Bornhuetter-Ferguson method]]
* [[Definition:Loss triangle]]
* [[Definition:Adverse development]]
* [[Definition:Actuarial opinion]]
{{Div col end}}

Definition:IBNR reserve - Revision history

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