Definition:Risks attaching basis
📋 Risks attaching basis is a reinsurance contract accounting and coverage basis under which the treaty responds to all underlying policies that incept — or attach — during the treaty period, regardless of when losses under those policies actually occur or are reported. If a cedant writes a twelve-month property policy on the last day of a risks-attaching reinsurance treaty, the reinsurer remains on risk for the full term of that underlying policy even though most of the exposure extends well beyond the treaty's nominal expiration date. This makes the basis fundamentally different from the losses occurring basis, where coverage depends on when the loss event happens relative to the treaty period rather than when the policy incepted.
⚙️ In practice, a risks attaching treaty creates a natural "run-off tail" because policies bound late in the treaty period continue generating exposure — and potentially claims — for months or even years afterward. Consider a quota share treaty on a risks attaching basis covering calendar year 2024: a marine cargo policy written on December 31, 2024, with a twelve-month term means the reinsurer is exposed through December 31, 2025. The cedant must track which policies incepted during the treaty period and allocate premiums and losses accordingly, which demands robust bordereaux reporting and administrative discipline. This basis is especially prevalent in proportional treaties and within the Lloyd's market, where syndicates historically operated on a three-year accounting cycle that naturally aligned with risks attaching logic. The Lloyd's year of account system, for instance, effectively functions on a risks attaching basis, with policies allocated to the year in which they were bound.
🧩 Why does the choice of basis matter so much? It directly shapes the reinsurer's exposure profile, earnings emergence, and reserving requirements. Because a risks attaching treaty captures all policies incepted during the period regardless of when claims manifest, the reinsurer's ultimate liability takes longer to become clear, making loss development patterns more extended and reserve estimation more complex. For the cedant, the basis affects how reinsurance recoveries align with its own underwriting year results, and mismatches between a cedant's internal accounting year and the reinsurance basis can complicate financial reporting. When negotiating treaty terms, brokers and underwriters must carefully consider whether a risks attaching or losses occurring structure better suits the portfolio's characteristics and the parties' appetite for tail risk.
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