Category: Claims handling · Reviewed by Chrissie Anderson, Client Executive · Last reviewed 2026-06-11
IBNER (Incurred But Not Enough Reported) reserves are the actuarial provisions for the expected further development of claims that have already been reported and reserved at the file level — capturing the tendency of case reserves to develop upward (or downward) before final closure.
IBNER is the difference between the sum of current case reserves on reported claims and the actuary’s projection of what those reported claims will ultimately cost. It is distinct from IBNR, which captures unreported claims; IBNER captures the further movement on reported claims.
Most reported claims develop upward over time. A property loss reported at £80,000 at FNOL frequently rises as the adjuster’s investigation uncovers depth of damage. A casualty injury claim reserved at £120,000 in year 1 may settle at £180,000 in year 3 once medical evidence stabilises. A professional indemnity claim with a £400,000 initial reserve may settle at £750,000 once counsel’s view, mediation dynamics and the litigation environment have crystallised. IBNER is the actuary’s quantification of this systematic upward drift.
IBNER, like IBNR, sits within the Solvency II technical-provisions framework. The probability-weighted average of all future cash flows for claims liabilities must include the expected further development of reported claims, not just the unreported ones. The PRA’s SS5/14 explicitly addresses the methodology, governance and disclosure of IBNER alongside IBNR.
Under IFRS 17, IBNER is part of the fulfilment cash flows. Movements in IBNER are part of the period’s insurance service result and are disclosed in the financial statements. Auditors examine IBNER methodology because it is one of the principal sources of unexpected reserve strengthening or release.
The Institute and Faculty of Actuaries’ Technical Actuarial Standards (in particular TAS 100 and TAS 200) impose principles-based requirements on the actuarial work that supports reserving, including documentation, judgment and review.
IBNER is calculated alongside IBNR but is typically derived from incurred-loss triangles (paid losses plus case reserves), not paid-loss triangles. The age-to-ultimate factors applied to the incurred triangle generate a projection of ultimate cost; the difference between projection and current incurred (= paid + case reserves) is the projected further development, which splits between IBNR (for unreported claims) and IBNER (for reported claims).
The split is sometimes derived from separate paid-development and case-reserve-development analyses, allowing the actuary to attribute movements to the right component. In long-tail lines, the IBNER component can be larger than the IBNR component, because reported claims continue developing for years after notification.
IBNER methodology pays particular attention to:
Actuaries triangulate by underwriting year and by class. Some firms also split IBNER between small and large claims; large claims often have an entirely different development curve.
IBNER is reviewed at each quarter-end exercise. Persistent upward movement in IBNER across multiple quarters is a signal that case reserves are systematically too low; persistent downward movement is a signal of over-prudence. Either pattern triggers a review of case-reserving methodology.
“Best-estimate IBNER” follows the actuary’s central projection. “Stressed IBNER” includes an explicit allowance for adverse scenarios — useful for risk reporting and capital modelling.
“Class-specific IBNER” is calculated by line of business, since development patterns differ sharply: motor own damage has near-zero IBNER (claims close quickly at predictable values), while latent abuse compensation claims may have IBNER that exceeds the original case reserves at twentieth or thirtieth development year.
“Negative IBNER” arises where case reserves systematically over-state ultimate. This is unusual but does occur where handler discipline has shifted toward conservative posting and the actuarial function is correcting downward.
“Per-claim IBNER” — rare in UK practice — assigns a development factor to each open claim based on the file’s age and complexity, generating a bottom-up IBNER estimate that can be compared with the top-down triangulation result.
A solicitors PI insurer’s 2022 underwriting year has 412 open claims at 30 June 2026. Aggregate paid losses on the year £14.3m; case reserves £24.6m; incurred to date £38.9m. The actuary’s Chain Ladder projection on incurred losses produces an ultimate of £46.4m for the year. Total expected further development £7.5m. Of this, the actuary’s IBNR/IBNER split (using historic patterns of late notification versus development on reported claims for the firm’s PI book) attributes £1.8m to IBNR (claims still to be reported, particularly given long-tail PI claim emergence) and £5.7m to IBNER (further development on the 412 reported claims). The actuary documents that the IBNER projection assumes 4% per annum claim inflation, no change in the firm’s mix of small versus large PI claims, and stable closure rates on the medical-evidence-dependent injury claims that overlap the PI book through derivative actions.
By Matt Bartlett, Director, on 2026-06-11. Next review: 2026-12-11.
This entry is part of the Apex Insurance Wiki. Last reviewed by Matt Bartlett on 2026-06-11. Apex Insurance Brokers Limited, FCA FRN 724952, Companies House 07014570. Not regulated advice — consult your broker on your specific position.
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