Executive Summary: Reinsurance Behind the Stop Loss: The Capital Structure Most TPAs Never See
LFP-02.05 — The Risk Layer#
Stop loss carriers do not retain all the risk they underwrite. They transfer portions to reinsurers through treaty and facultative arrangements that are invisible to employers, brokers, and TPAs but that directly determine stop loss availability, pricing stability, and market capacity. Treaty reinsurance is a standing agreement covering all qualifying stop loss policies within defined parameters, automatic and without individual negotiation. Facultative reinsurance covers individual groups or high-cost members that fall outside treaty parameters, negotiated case by case at higher cost. The two primary structures are quota share, under which the reinsurer takes a fixed percentage of every policy and pays that same percentage of claims, and excess of loss, under which the reinsurer pays claims above a defined threshold on the carrier’s aggregate book.
The institutions providing this capital are primarily global in scope. Lloyd’s of London syndicates access the U.S. stop loss market through managing general agents. Bermuda-domiciled reinsurers including RenaissanceRe, Everest Group, and PartnerRe participate through excess of loss treaties. Swiss Re Americas, Munich Re US, and General Re fill additional capacity. Behind these reinsurers sits a retrocession layer. An employer purchasing a $50,000 specific attachment point may be four or five steps removed from the entity ultimately bearing the catastrophic risk. Each layer takes a portion of the premium and assumes a portion of the risk; each layer also introduces a dependency that the employer cannot monitor.
The transmission mechanism from global capital markets to the employer’s renewal quote follows a predictable cycle. In a soft reinsurance market, capacity is abundant, pricing is competitive, and stop loss carriers can write policies at lower cost. In a hard market, capacity restricts, pricing increases, and stop loss carriers face higher costs that flow to employers through premium increases, higher minimum attachment points, and more aggressive laser application. The pandemic deferred care surge, sustained medical cost trend acceleration, and catastrophic loss events in other lines of business sharing reinsurer capital have all contributed to the corrective pricing cycle that produced 8.8% to 10.5% annual stop loss premium increases documented in the 2025 Aegis survey. Oliver Wyman and Guy Carpenter reported stop loss loss ratios deteriorating from 79.5% in 2018 to 80.3% in 2023; the employer-facing price increase partially reflects reinsurance cost pass-through that neither the employer nor the broker can directly observe.
The AM Best rating of a stop loss carrier is the employer’s primary available proxy for the question they should be asking: does this carrier have adequate capital and reinsurance depth to pay claims if multiple specific events hit simultaneously? Carrier solvency is a concentration risk the market does not transparently disclose; reinsurance treaty terms, carrier loss ratios by segment, and reinsurance market concentration data are not available to the employer-facing market. The employer making the stop loss purchase decision does so without visibility into the capital structure that ultimately supports the stop loss promise.