hardConceptDesignMidSeniorStaff
What is a loss development triangle, and what does the actuary need from your claims system that reporting does not?
A loss development triangle groups claims by accident or underwriting period and development age so actuaries can estimate ultimate cost, IBNR and reserve movement. It needs immutable claim transactions, evaluation-date reconstruction and clear paid versus incurred measures.
5 min readUpdated 2026-08-15
Answer
Short answer
A loss development triangle shows how claim costs mature over time. Rows are accident, underwriting or report periods; columns are development ages such as 12, 24 and 36 months. Actuaries use the pattern to estimate ultimate loss, IBNR and reserves, so the claims system must preserve immutable transactions and rebuild the book exactly as it stood at any evaluation date.
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Likely follow-ups
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