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📊 '''Accident year combined ratio''' is a profitability metric used by [[Definition:Insurance carrier | insurance carriers]] and [[Definition:Reinsurance | reinsurers]] that measures underwriting performance by matching [[Definition:Loss | losses]] and [[Definition:Loss adjustment expense (LAE) | loss adjustment expenses]] to the [[Definition:Policy period | policy period]] in which the underlying claims actually occurred, rather than to the period in which they were reported or paid. Unlike the [[Definition:Calendar year combined ratio | calendar year combined ratio]], which reflects all reserve movements booked during a fiscal year regardless of origin, the accident year metric isolates the economic result of business written in a specific period. This distinction makes it a purer gauge of [[Definition:Underwriting | underwriting]] quality, stripping away the noise created by favorable or adverse [[Definition:Reserve development | reserve development]] on prior years.

⚙️ To construct this ratio, actuaries and financial analysts assign each [[Definition:Claim | claim]] to its accident year — the twelve-month window in which the loss event took place — and pair the resulting incurred losses with the [[Definition:Earned premium | earned premiums]] attributable to that same period. The [[Definition:Loss ratio | loss ratio]] component captures incurred losses and LAE divided by earned premiums, while the [[Definition:Expense ratio | expense ratio]] adds [[Definition:Underwriting expense | underwriting expenses]] such as [[Definition:Acquisition cost | acquisition costs]] and operational overhead. Because many claims, particularly in long-tail lines like [[Definition:General liability insurance | general liability]] or [[Definition:Professional liability insurance | professional liability]], take years to fully develop, the accident year combined ratio for a recent period is initially based on [[Definition:Incurred but not reported (IBNR) | IBNR]] estimates and is revised as actual claims experience emerges. Regulatory and accounting frameworks — whether [[Definition:US GAAP | US GAAP]], [[Definition:IFRS 17 | IFRS 17]], or regional statutory standards — differ in how they prescribe or permit the presentation of accident year data, but the underlying concept remains consistent across markets.

🔍 Investors, [[Definition:Rating agency | rating agencies]], and [[Definition:Buy-side analyst | buy-side analysts]] prize the accident year combined ratio precisely because it reveals whether current pricing and risk selection are generating sustainable profits before the flattering — or alarming — effects of prior-year reserve adjustments. A carrier might post an attractive calendar year combined ratio simply because it released redundant reserves set aside years ago, masking a deteriorating current book. The accident year view exposes that deterioration. During [[Definition:Earnings call | earnings calls]] and in [[Definition:Statutory filing | statutory filings]], sophisticated market participants routinely ask for accident year data by line of business, and divergence between accident year and calendar year results often triggers deeper scrutiny of a company's [[Definition:Reserving | reserving]] practices and [[Definition:Pricing adequacy | pricing adequacy]].

'''Related concepts:'''
{{Div col|colwidth=20em}}
* [[Definition:Calendar year combined ratio]]
* [[Definition:Combined ratio]]
* [[Definition:Loss ratio]]
* [[Definition:Reserve development]]
* [[Definition:Incurred but not reported (IBNR)]]
* [[Definition:Expense ratio]]
{{Div col end}}

Definition:Accident year combined ratio - Revision history

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