Definition:Stop loss treaty (also aggregate stop loss)
📋 Stop loss treaty (also aggregate stop loss) is a form of reinsurance contract that protects a ceding insurer against aggregate losses exceeding a predetermined threshold over a defined period, typically expressed as a percentage of the cedant's net earned premium or as an absolute monetary amount. Unlike per-risk or per-occurrence excess of loss treaties — which respond to individual large losses or single catastrophic events — a stop loss treaty addresses the cumulative weight of losses across an entire portfolio or line of business during the treaty period, regardless of whether any individual claim is particularly large. This makes it a powerful tool for protecting against attritional loss deterioration, adverse frequency trends, or a combination of moderate events that collectively erode profitability.
⚙️ The mechanics involve the cedant retaining aggregate losses up to the attachment point — say, 80% of net earned premium — after which the reinsurer begins to pay a share of losses, typically up to a specified ceiling (for example, 120% of net earned premium). The treaty usually covers a twelve-month accident year or underwriting year, and the final settlement depends on the cedant's actual loss ratio once all claims within the period are developed and valued. Because the reinsurer's exposure is tied to the cedant's overall underwriting result rather than to discrete events, stop loss treaties require careful definition of subject premium income, loss development protocols, and reporting standards. Pricing is complex: actuaries must model the full distribution of the cedant's aggregate loss ratio, often using stochastic simulation, to estimate the probability and expected severity of breaching the attachment point. The treaty may also include provisions for loss corridors or co-participation, where the cedant retains a percentage of losses even within the reinsured layer, aligning incentives and limiting moral hazard.
🛡️ For cedants, a stop loss treaty provides a stabilizing backstop that smooths earnings volatility and protects solvency in adverse years — particularly valuable for smaller or mid-sized insurers whose portfolios may lack the diversification to absorb unexpected aggregate loss spikes. Regulators and rating agencies generally view stop loss protections favorably, as they reduce the probability of severe capital impairment. However, reinsurers approach this product with caution because it exposes them to the cedant's entire portfolio management decisions, creating significant information asymmetry. As a result, stop loss treaties tend to carry relatively high pricing margins and are often written only where the reinsurer has deep familiarity with the cedant's book. They are also subject to careful scrutiny under accounting standards — under both US GAAP (SSAP 62R) and IFRS 17, a contract must transfer sufficient insurance risk to qualify for reinsurance accounting treatment, and stop loss treaties that cap the reinsurer's exposure too tightly may fail this test and be reclassified as financing arrangements.
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