Category: Reinsurance structures · Reviewed by Mark Fox, Broker · Renewals · Last reviewed 2026-06-05
Aggregate excess of loss (agg XL) reinsurance responds to the aggregate of all losses on a defined portfolio during the treaty year, where the aggregate exceeds the annual aggregate deductible (AAD). Unlike per-risk or per-event XL, the trigger is the cumulative loss experience over the year, not any single loss or event.
Category: Reinsurance structures Also known as: agg XL, aggregate XL Related concepts: stop loss reinsurance, excess of loss reinsurance, aggregate cover
In an agg XL the cedant retains the first £x (the annual aggregate deductible) of all losses in the year falling within the treaty scope, with the reinsurer responding to the next £y (the limit). The retention may be expressed in absolute terms (£40m AAD) or as a percentage of premium (95 per cent loss ratio aggregate retention). Individual losses below an event minimum (the ‘franchise’) are typically excluded from aggregation.
Agg XL is often used as a ‘top-up’ to per-risk and per-event XL programmes, providing additional protection against an unusually adverse year — for example, multiple medium-sized events that individually fall below the cat XL retention but collectively exceed the cedant’s risk appetite.
Agg XL contracts are documented under the Market Reform Contract format. They are subject to general principles of English contract law and the Insurance Act 2015. Solvency II treats agg XL as risk mitigation in proportion to the expected reduction in the cedant’s net loss distribution.
Agg XL is particularly useful where the cedant faces multiple smaller-event accumulation losses that are unlikely individually to exhaust per-event XL but cumulatively produce an adverse result. Common applications include: UK windstorm where multiple smaller storms (each below cat XL retention) collectively impact the year; crop reinsurance with frequent small weather events; and motor reinsurance with adverse frequency development.
The pricing of agg XL is typically informed by stochastic modelling of the cedant’s annual loss distribution, with attention to tail behaviour. Reinsurers price for the expected loss in the layer plus a margin reflecting the volatility of the underlying portfolio.
An illustrative example: a UK home insurer purchases agg XL of £30m in excess of £50m aggregate during 2024, with an event minimum of £2m. In 2024 the cedant suffers seven storm events each producing aggregate losses of £8m–£12m (total £65m), all individually below the £15m cat XL retention. The agg XL responds for £15m (£65m − £50m), reducing the cedant’s net loss to £50m.
This entry is part of the Apex Insurance Wiki. Last reviewed by Matt Bartlett on 2026-06-05. Next review: 2026-12-05.
Apex Insurance Brokers Limited. Authorised and regulated by the Financial Conduct Authority, FRN 724952. Registered in England and Wales, Companies House 07014570. This entry provides general information about UK insurance concepts and is not regulated advice. Consult your insurance broker on your specific position.
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