IBNR (Incurred But Not Reported)

IBNR is the actuarial reserve an insurer establishes for claims that have happened but the company doesn't yet know about individually — plus, in most modern usage, the expected future development on claims already reported (sometimes called IBNER, 'incurred but not enough reported'). Because losses can occur well before anyone files a claim, an insurer cannot rely only on case reserves, which exist only for known claims. IBNR is an estimate across the whole book, calculated with actuarial methods, and it combines with paid losses and case reserves to produce total incurred losses and the projected ultimate loss.

IBNR matters less to a small-business buyer at the individual-policy level and more as an indicator of an insurer's financial health and pricing discipline. Carriers that under-reserve IBNR can appear more profitable than they are, then face reserve strengthening that hardens the market and drives up your renewal. Long-tail lines you may carry — general liability, professional liability, and workers' comp — carry the heaviest IBNR because claims from those coverages can surface years after the policy period, especially for latent injuries or claims-made exposures.

A practical nuance: IBNR is why the current policy year's losses are treated as immature and are not fully credible for pricing — a large chunk of that year's ultimate cost is still hiding in IBNR. It also underpins the value of a retroactive date and tail coverage on claims-made policies, since late-reported claims are exactly what IBNR anticipates. When comparing carriers, a history of adverse IBNR development is a red flag about reserve adequacy, whereas consistently favorable development suggests conservative, dependable reserving.