Both structures transfer part of an insurer’s business to a reinsurer, but they solve different portfolio problems. Quota share is simple and broad. Surplus is more selective because smaller risks can remain fully retained while larger risks are ceded in increasing proportions.
Munich Re’s reinsurance glossary defines quota share as a pro rata arrangement in which the reinsurer assumes an agreed percentage of each insured risk and shares premiums and losses accordingly. It describes surplus as pro rata protection for the amount above the ceding company’s chosen net retention.
Quota share: one percentage across covered risks
Suppose an insurer writes a 40% quota-share treaty. Subject to the contract, the insurer keeps 60% of each covered risk and cedes 40% to the reinsurer. The reinsurer receives 40% of the subject premium and is responsible for 40% of covered losses.
The important idea is consistency: the same contractual percentage applies across the defined portfolio, subject to treaty limits and terms.
Surplus reinsurance: the percentage changes with risk size
Surplus reinsurance starts with the insurer’s retention, often called a line. Risks at or below that retained amount may stay entirely with the insurer. When a risk exceeds the retention, the insurer can cede the surplus up to the treaty’s capacity, commonly expressed as a number of lines.
Because the ceded amount depends on the size of each risk, the reinsurance percentage changes from policy to policy.
| Feature | Quota share | Surplus |
|---|---|---|
| Ceded percentage | Fixed for covered business | Varies by individual risk |
| Small risks | A fixed share is still ceded | May be fully retained below the retention |
| Large risks | Same percentage, subject to treaty limit | Larger share can be ceded up to treaty capacity |
| Portfolio effect | Reduces exposure across the whole covered book | Smooths differences in individual risk size |
| Premium and loss sharing | Same fixed ratio | Ratio follows the cession on each risk |
A simplified quota-share example
An insurer writes a $1,000,000 policy under a 30% quota-share treaty. Ignoring other treaty details, it retains $700,000 of the risk and cedes $300,000. If a covered loss is $200,000, the proportional split would be $140,000 to the insurer and $60,000 to the reinsurer.
The same 30/70 relationship would apply to other covered risks in the treaty, within the contractual limits.
A simplified surplus example
Assume an insurer chooses a $1,000,000 retention and buys a four-line surplus treaty. The treaty can accept up to four times the retention, or $4,000,000 of surplus capacity in this simplified example.
- A $750,000 risk can be fully retained because it is below the $1,000,000 line.
- A $2,000,000 risk can be 50% retained and 50% ceded.
- A $5,000,000 risk can be $1,000,000 retained and $4,000,000 ceded, subject to the treaty and risk meeting its terms.
The percentages are therefore 0%, 50% and 80% ceded in these three examples—unlike quota share, where one fixed percentage would apply.
Why insurers use quota share
- Support growth by sharing risk and premium across a portfolio.
- Reduce net exposure in a simple, predictable proportion.
- Obtain underwriting or capacity support from a reinsurer.
- Manage capital and volatility, subject to regulatory and accounting treatment.
Why insurers use surplus reinsurance
- Retain smaller risks while ceding a larger proportion of peak risks.
- Create a more balanced net portfolio when policy sizes vary widely.
- Control net retention on large individual risks without ceding the same percentage of every small risk.
Proportional is not the same as excess of loss
Quota share and surplus divide premium and loss proportionally. Excess-of-loss reinsurance is non-proportional: it responds when covered losses exceed an agreed retention or attachment point, up to a limit. An insurer can use proportional and non-proportional treaties together in one reinsurance program.
Ceding commission and treaty economics
Because the primary insurer incurs acquisition and administration expenses, proportional treaties commonly include a ceding commission. The commission structure can be fixed, sliding or otherwise negotiated. Actual treaty economics are much more complex than the simplified risk-sharing examples above.
Frequently asked questions
Is surplus reinsurance the same as excess-of-loss reinsurance?
No. Surplus is proportional (pro rata) reinsurance. Excess of loss is non-proportional.
Does quota share use the same percentage for every risk?
Within the defined treaty scope, the contractual quota is fixed, subject to limits, exclusions and other terms.
What is a “line” in surplus reinsurance?
It commonly refers to the insurer’s chosen retention on a risk. Treaty capacity can be expressed as a multiple of that line.
Can an insurer combine quota share with excess-of-loss protection?
Yes. Reinsurance programs commonly layer different structures to address different kinds of volatility and capital needs.
Sources & further reading
Reviewed against established reinsurance reference material in September 2026. Examples are simplified for education; actual treaty wording, accounting, commissions and capacity provisions control.
