Definition:Surplus share
🔄 Surplus share is a type of proportional (pro rata) reinsurance arrangement in which the ceding insurer retains a fixed dollar amount of liability on each risk — known as the retention or "line" — and cedes the portion of each risk that exceeds that retention to the reinsurer, up to specified limits expressed as multiples of the retention. Unlike a quota share, where every risk is split by a single percentage, a surplus share treaty allows the ceding company to keep 100 percent of smaller risks while transferring a larger proportion of bigger ones.
📐 Consider a surplus share treaty with a retention of $500,000 and a capacity of four lines, giving the reinsurer a maximum per-risk limit of $2 million. If the ceding company writes a policy with a sum insured of $1.5 million, it retains $500,000 (one line) and cedes the remaining $1 million to the reinsurer. Premium and losses are divided in the same proportion — one-third retained, two-thirds ceded. On a smaller policy of $400,000, the entire risk falls within the retention, so no premium or loss passes to the reinsurer at all. This variable cession percentage is calculated risk by risk, making surplus share treaties more administratively complex than quota shares but far more efficient in targeting the risks that actually require risk transfer.
💡 The strategic appeal of surplus share arrangements lies in their precision. A property insurer writing a mix of residential and commercial risks can retain affordable exposures in full — preserving the associated underwriting profit — while offloading the large commercial accounts that could distort its loss ratio. For MGAs negotiating capacity with carrier partners, understanding how surplus share treaties shape a carrier's net retained book is essential to aligning program economics. The mechanism also underpins treaty reinsurance structures at Lloyd's, where syndicates routinely use surplus share placements to manage line-size volatility.
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