IBNER (Incurred But Not Enough Reported)

Reviewed by Apex Insurance Brokers · Last reviewed 2026-06-22

Reviewed by Apex Insurance Brokers · Last reviewed 2026-06-22

Category: Actuarial fundamentals · Reviewed by Chrissie Anderson, Client Executive · Last reviewed

IBNER

Incurred But Not Enough Reported (IBNER) is the difference between the ultimate cost of reported claims and the case reserves currently held on those claims. It captures the development on known claims, separately from pure IBNR (genuinely unreported claims).

Why it matters

Case reserves on reported claims tend to develop upwards over time as facts emerge — particularly in long-tail liability where:

• Medical prognoses worsen.
• Quantum revisions follow JC Guidelines updates.
• Defendant solicitors revise estimates after disclosure.
• Court awards exceed initial expectations.

A reserving exercise that estimates only pure IBNR and trusts case reserves on reported claims for their face value will systematically under-reserve.

Measurement

IBNER is typically estimated via:

• Reported (incurred) chain ladder — develops case reserves alongside paid losses, implicitly capturing IBNER.
• Average cost per claim methods — projects ultimate severity per claim and subtracts paid + case reserves.
• Generalised linear models at individual claim level.

Reporting

Many insurers present a single combined IBNR figure (broad IBNR = pure IBNR + IBNER) in financial statements, while disaggregating internally for reserving sub-committee scrutiny.

References

• IFoA. General insurance reserving practical guides.
• Friedland, J. (CAS, 2010).

Cross-references

• Incurred but not reported
• IBNR
• Loss development

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