Reinsurance: Definition and How It Works

Reinsurance is a contract by which one insurance company (the ceding company, or cedant) transfers a defined portion of its insurance risk to another insurer (the reinsurer) in exchange for a corresponding share of the original premium. Reinsurance is often summarized as "insurance for insurers": it allows primary carriers to spread catastrophic or concentrated exposures across the global risk-bearing market, stabilize underwriting results, and expand their capacity to write new business. The legal relationship between cedant and reinsurer is governed by the reinsurance treaty or certificate — the original policyholder has no direct rights against the reinsurer unless a "cut-through" endorsement has been negotiated.

How Reinsurance Works

When a primary insurer underwrites a policy, it assumes the obligation to pay covered losses up to the policy limits. If those limits are large — or if many policies share a common catastrophic exposure (a hurricane, a wildfire, a pandemic) — the insurer's surplus (the excess of assets over liabilities) can be threatened by a single adverse event. Reinsurance addresses this by shifting a portion of both the premium and the loss obligation to one or more reinsurers.

Core mechanics:

  1. The ceding company pays a cession premium — the reinsurer's share of the original premium, less a ceding commission paid back to the cedant to help cover acquisition and overhead costs.
  2. In exchange, the reinsurer agrees to pay its contractual share of covered losses as they occur.
  3. The ceding company remains the policyholder's counterparty; claims are handled and paid by the primary insurer, which then seeks reimbursement from its reinsurers.

Treaty vs. Facultative Reinsurance

Treaty reinsurance is an agreement under which the reinsurer automatically accepts all risks of a described class written by the cedant over the treaty period — no individual underwriting approval is required. Treaties are the most common form of reinsurance and typically run for one year, renewing annually.

Facultative reinsurance covers a single, individually negotiated risk. The cedant submits a specific risk to one or more reinsurers, each of whom underwrites it independently and may accept or decline. Facultative placement is used when a risk exceeds treaty capacity, falls outside treaty eligibility, or presents unusual characteristics the cedant wants to specifically exit. Brokers placing large or complex commercial accounts often rely on facultative capacity when standard treaty limits are insufficient — see How to Place a Hard-to-Insure Risk in the Surplus Lines Market for related placement strategy.

Proportional vs. Non-Proportional Structures

Reinsurance arrangements fall into two broad structural categories:

Proportional (pro-rata) reinsurance: The reinsurer shares a fixed percentage of every premium dollar and every loss dollar within a defined class.

  • Quota share: The cedant cedes a flat percentage (e.g., 30%) of every policy in a defined portfolio; the reinsurer receives 30% of premiums and pays 30% of every loss.
  • Surplus share: The cedant retains a fixed "line" (e.g., $1 million) and cedes the portion above its retention up to a maximum number of additional lines; the cession percentage varies policy by policy based on the relationship between the policy limit and the cedant's retention.

Non-proportional (excess-of-loss) reinsurance: The reinsurer pays only losses that exceed a specified retention — the cedant bears all losses up to that threshold.

  • Per-occurrence excess of loss: Applies to each individual loss event; the reinsurer pays the portion of any single occurrence loss that exceeds the cedant's retention.
  • Per-risk excess of loss: Applies to losses from a single insured risk rather than a single event.
  • Aggregate (stop-loss) excess of loss: Triggered when the cedant's total losses for a period exceed a defined aggregate threshold; similar in concept to the aggregate stop-loss coverage used in self-funded health plans — see Stop-Loss Insurance for Self-Funded Health Plans.
  • Catastrophe (cat) excess of loss: Covers losses from a single catastrophic event (hurricane, earthquake, terrorism) that aggregate beyond the cedant's per-occurrence retention.

Retrocession

A reinsurer may itself purchase reinsurance — transferring risk it has accepted from cedants to another carrier. This arrangement is called a retrocession, and the accepting company is the retrocessionaire. Retrocession allows the global reinsurance market to diversify large single-event exposures across many carriers worldwide.

Why Reinsurance Matters for Insurance Brokers

Commercial brokers are not direct parties to reinsurance treaties, but reinsurance availability and pricing heavily influence what primary carriers can offer:

  • Capacity constraints: When reinsurers tighten capacity — reducing limits they will accept or excluding specific perils — primary carriers must reduce their per-risk limits or exit lines of business entirely. Brokers building layered towers (see Excess Casualty Layered Towers in 2026) often feel reinsurance constraints most acutely in the excess layers.
  • Carrier financial strength: A primary carrier's ability to honor claims depends partly on its reinsurance program. AM Best ratings incorporate reinsurance usage and quality when scoring a carrier's financial strength; a carrier with a weak or uncollectible reinsurance panel is more vulnerable to surplus depletion after a large loss.
  • Cut-through endorsements: In large commercial placements, insureds sometimes negotiate a cut-through clause giving them a direct claim against the reinsurer if the cedant becomes insolvent — a structural protection analogous to the statutory guaranty-fund backing that admitted carriers provide through state solvency regulation.
  • Captive programs: Captive insurance companies often purchase reinsurance for losses above the captive's retention — using reinsurance to extend the risk-financing structure beyond what the captive's surplus can absorb. See Captive Insurance for how this integrates with a broader risk-financing strategy.

Related Terms

  • Admitted Carrier — a primary insurer licensed by the state; reinsurers typically operate outside state rate-and-form regulation and are evaluated primarily on financial strength
  • AM Best Rating — financial strength rating that incorporates a carrier's reinsurance recoverables and panel quality
  • Captive Insurance — a risk-financing alternative that frequently relies on reinsurance to cap catastrophic exposure
  • Self-Insured Retention — the per-claim amount a policyholder retains before the primary policy responds; analogous in structure to the cedant's retention in an excess-of-loss treaty
  • Ceding commission — the allowance paid by the reinsurer to the cedant under a proportional treaty to reimburse the cedant's acquisition costs and overhead
  • Retrocession — reinsurance purchased by a reinsurer; the mechanism by which risk disperses through the global reinsurance market

How Brokers Use This Term in Practice

Insurance brokers encounter reinsurance in three primary contexts. First, when explaining capacity limitations to insureds — if a carrier cannot offer a $50M occurrence limit on a single risk, the underlying reason is often that the carrier's treaty provides only $25M of per-risk reinsurance support, constraining what it can confidently underwrite. Second, when evaluating carrier options: a carrier relying heavily on reinsurance recoverables to support its balance sheet is more exposed to reinsurer credit risk than one with a conservative, high-quality panel. Third, when structuring captive or large deductible programs where reinsurance behind the captive or retention layer must be priced and placed to complete the risk-transfer structure.

Arvori helps insurance brokers understand carrier capacity constraints, reinsurance-driven market cycles, and risk-financing structures for complex commercial accounts. Learn more about Arvori's tools for insurance professionals.