Treaty Reinsurance
Also known as: reinsurance treaty, obligatory reinsurance
Treaty reinsurance is a standing contract in which a reinsurer agrees, in advance, to accept a defined share of an insurer's entire book of business — for example, all of its workers' compensation or commercial property policies. Unlike facultative coverage, the reinsurer does not review each risk; it is obligated to take every policy that meets the treaty's terms. This makes treaty the workhorse of the reinsurance market, giving carriers automatic, predictable capacity so they can bind everyday accounts quickly and confidently.
For a small-business buyer, treaty reinsurance is the reason ordinary policies get issued fast and at stable prices. Because the primary insurer knows its treaty will absorb part of every loss, it can quote and bind without special approval for each account. Treaties come in two families: proportional (quota-share or surplus-share, where premium and losses split by a set percentage, usually with a ceding commission) and non-proportional excess-of-loss (the reinsurer pays only above an attachment point). The mix a carrier chooses affects how much surplus it must hold and, indirectly, the rates it charges.
A practical nuance is that treaties are renegotiated periodically — often annually at January 1 — and their cost is a major driver of primary market cycles. When reinsurers raise treaty pricing after heavy catastrophe losses, primary carriers face a hard market and pass increases to policyholders even when individual accounts are loss-free. Carriers still keep facultative reinsurance available for risks that exceed treaty limits or hit treaty exclusions, so the two structures work in tandem rather than as substitutes.
Real-world scenario
Cornerstone Mutual, a regional carrier writing small-business property policies, expects to book $60,000,000 in premium this year across roughly 12,000 policies with an average building limit of $850,000. Rather than negotiating protection policy-by-policy the way facultative reinsurance works, Cornerstone buys a single treaty that automatically covers its entire book. It places a property excess-of-loss treaty that pays $4,000,000 in excess of a $1,000,000 retention per loss, for an annual reinsurance premium of $3,600,000.
In September a warehouse fire produces a covered loss of $3,850,000. Cornerstone pays the insured, absorbs the first $1,000,000 itself (its attachment point), and the treaty reinsurer reimburses $2,850,000. Two months later a hailstorm drives 140 claims totaling $9,200,000; because each individual claim falls under the $1,000,000 retention, the per-risk treaty pays nothing, which is why Cornerstone also carries a catastrophe layer of $15,000,000 excess of $5,000,000 for aggregated events.
On its quota-share treaty, Cornerstone cedes 30% of premium — $18,000,000 — and in exchange receives a ceding commission of $5,400,000 (30%) to offset acquisition costs. That commission, plus the reinsurance recoverables, protects Cornerstone's policyholder surplus and lets a $60,000,000 carrier write like one twice its size.
How it affects your premium
Treaty reinsurance is priced on the ceding company's whole portfolio, so the cost reflects how volatile and well-managed that entire book is, not a single risk:
- Loss experience of the ceded book — the reinsurer studies several years of loss runs and loss development; a book with frequent large fires or catastrophe losses pays a far higher rate on line.
- Retention and attachment point — the lower the ceding insurer's per-loss retention, the more losses pierce the treaty and the higher the premium; raising the attachment point lowers cost.
- Treaty structure (quota share vs. excess of loss) — proportional quota-share deals share premium and losses by a fixed percentage, while non-proportional excess-of-loss layers charge for the tail risk above the retention.
- Ceding commission negotiated — a richer ceding commission returned to the insurer effectively raises the net cost of the coverage to the reinsurer and is priced in.
- Catastrophe exposure and geographic concentration — coastal wind, wildfire, and earthquake accumulation drive cat-layer pricing more than any other factor.
- Reinsurer capacity and the market cycle — hard-market years with scarce capital push rates up across every treaty regardless of individual performance.
- Quality of the cedent's underwriting and controls — disciplined underwriting, strong data, and clean audits earn better terms and lower rates on line.
Common misconceptions
Myth: Treaty reinsurance is something a normal business buys to protect its own operations.
Reality:
No — treaty reinsurance is bought by insurance companies to protect their own balance sheets, not by ordinary businesses. A restaurant or contractor buys primary coverage; only the insurer behind that policy cedes risk under a treaty.
Myth: A treaty covers every single policy and loss the insurer writes.
Reality:
Treaties cover a defined class of business subject to limits, exclusions, and a per-loss retention. Losses below the attachment point stay with the ceding company, and risks outside the treaty's scope must be placed with facultative reinsurance instead.
Myth: Treaty and facultative reinsurance are basically the same thing.
Reality:
They are different tools. A treaty automatically covers a whole portfolio negotiated once a year, while facultative reinsurance is placed one risk at a time for unusual or oversized exposures.
Frequently asked questions
Who actually buys treaty reinsurance?
Insurance companies — including small regional carriers, mutuals, and even a large captive insurance program — buy treaty reinsurance to cap their exposure on an entire class of business rather than risk-by-risk.
What is the difference between quota-share and excess-of-loss treaties?
A quota-share treaty is proportional: the reinsurer takes a fixed percentage of every premium and loss. An excess-of-loss treaty is non-proportional and only responds once a loss exceeds the ceding insurer's per-occurrence retention.
Does treaty reinsurance change my policy as the insured business?
No. Your policy terms, limits, and claims process are unchanged; reinsurance is a private arrangement between your insurer and its reinsurer that you never see on your coverage documents.
How does a ceding commission work in a treaty?
Under a proportional treaty the reinsurer pays the ceding company a ceding commission — a percentage of the premium it receives — to reimburse the insurer for the acquisition and administrative costs of writing that business.
Can an insurer exit a treaty before the losses fully develop?
Yes. Parties can agree to a commutation, settling all future obligations for a lump sum, or move a block of run-off liabilities through a loss portfolio transfer.
Sources cited
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