Published October 2026.
Direct Answer: A quota share treaty cedes a fixed percentage of every risk — a 50% quota share hands the reinsurer half of every premium and half of every loss, whatever the size of the risk. A surplus share treaty instead measures each risk against the cedent’s retention in “lines”: a 9-line surplus treaty on a $200,000 retention automatically absorbs up to nine multiples of the retention ($1.8 million) above what the cedent keeps, so small risks barely touch the reinsurer while large ones lean on it heavily. The practical difference is flexibility: quota share is a constant slice, surplus share is a capacity band that expands and contracts with each line.
Reading Your Treaty Slip
Every proportional treaty slip answers the same three questions: what the cedent keeps, what the reinsurer takes, and how the two are measured. In a quota share, the measurement is a percentage fixed at inception and applied to every risk. In a surplus share, it is a multiple of the cedent’s retention, expressed in lines. Both are proportional treaties — premium and losses shared in the same ratio as the sums insured — which separates them from excess-of-loss covers that respond only above a threshold. They sit inside the broader family of reinsurance treaty structures, and both solve the same problem: how carriers transfer risk to reinsurers without giving up the business they want to keep.
Three terms do most of the work. The cedent hands risk over. The retention is what it keeps. The cession is what passes to the reinsurer.
Quota Share: One Fixed Percentage for Everything
How the percentage works
A quota share treaty states a single cession percentage — 50%, 70%, 30% — applied to every risk bound under it. At 50%, the reinsurer receives half the premium on each policy and pays half of each loss; the cedent keeps the other half of both. The percentage does not move with risk size or loss history: a $100,000 homeowners line and a $5 million commercial account split identically, so a junior underwriter reading “50% quota share” knows the cedent’s net position on any covered risk with no further calculation.
Worked example: a 50% quota share on a $2M line
Take a commercial property risk with a $2,000,000 sum insured under a 50% quota share:
- Cedent retains: 50% × $2,000,000 = $1,000,000
- Reinsurer takes: 50% × $2,000,000 = $1,000,000
A $400,000 fire loss splits the same way: $200,000 each. No threshold, no per-risk limit. On a $20,000 gross premium, the reinsurer receives $10,000 and the cedent keeps $10,000, less any ceding commission.
Surplus Share: Lines, Not Percentages
What a line actually is
A surplus treaty replaces the fixed percentage with a retention in currency and capacity in multiples of that retention. Each multiple is a line. With a $200,000 retention, one line equals $200,000, and a “9-line surplus treaty” provides nine lines — $1,800,000 — of capacity above the retention. The reinsurer automatically accepts each risk’s portion above the retention up to the line limit, so the cession percentage is derived risk by risk from the line size rather than fixed on the slip.
Worked example: a $1M line on a 9-line surplus treaty with a $200k retention
Bind a $1,000,000 commercial risk under a 9-line surplus treaty with a $200,000 retention:
- Retention: $200,000 (1 line — stays with the cedent)
- Cession: $1,000,000 − $200,000 = $800,000 (4 lines — to the reinsurer)
- Lines used: 5 of the 9 available
- Effective split: cedent 20%, reinsurer 80%
Premium divides the same way: 80% follows the $800,000 to the reinsurer. A $600,000 loss on the risk costs the cedent $120,000 (20%) and the reinsurer $480,000 (80%) — the loss follows the sum-insured split exactly. The difference from quota share is only that the split was computed from the line size rather than read off the slip.
Small risks stay home
A $150,000 risk under that treaty sits below the $200,000 retention: zero lines used, nothing ceded, 100% retained. The identical risk under a 50% quota share would hand $75,000 of sum insured, half the premium, and half of every loss to the reinsurer. For a book of small, profitable risks with a tail of large ones, surplus protects capacity where needed and leaves the good small business alone. The complete guide to reinsurance treaties counts surplus share among the core proportional forms for exactly this reason.
Why Surplus Flexes With Line Size While Quota Share Does Not
Side by side on the same book
The same three risks under both structures:
- $150,000 risk: quota share cedes $75,000 (50%); surplus cedes $0 (below retention).
- $1,000,000 risk: quota share cedes $500,000 (50%); surplus cedes $800,000 (80%).
- $2,000,000 risk: quota share cedes $1,000,000 (50%); surplus cedes $1,800,000 (90%, capped at 9 lines).
The quota share’s cession never moves. The surplus treaty’s effective cession climbs from 0% to 80% to 90% as the line grows — a sliding scale built out of fixed lines, which is why brokers call surplus “automatic facultative.” The trade-off is administration: quota share needs no per-risk scheduling, while surplus requires every risk measured in lines and bordereau-reported. Cedents accept the paperwork because the economics favor mixed-size books — they stop paying reinsurance premium on risks they could retain. In hard markets, when hard-market pricing pressure makes every ceded premium dollar expensive, that efficiency often tips the choice toward surplus.
When the Line Exceeds the Treaty Limit
Worked example: a $3M line against a 9-line treaty with a $200k retention
Take a $3,000,000 risk against the same treaty. Maximum cession is 9 × $200,000 = $1,800,000:
- Cedent retention: $200,000 (1 line)
- Treaty cession: $1,800,000 (9 lines — the treaty maximum)
- Excess over treaty limit: $1,000,000 — outside the treaty entirely
A $900,000 loss apportions by share of the total sum insured: treaty reinsurer $540,000 (60%), facultative placement $300,000 (33.3%), cedent $60,000 (6.7%).
Facultative cover or outright retention
The $1,000,000 excess has two homes. The usual one is facultative reinsurance: the broker places that specific layer before the policy is bound, so the line is fully protected on day one. The alternative is outright retention, which only makes sense when the balance sheet can absorb a total loss on that slice. The surplus treaty itself never stretches — nine lines is a hard cap. Large facultative placements are also where accumulation and probable maximum loss discipline matters most, since each individually placed layer still aggregates into peak exposures. Most are arranged in the January renewal season alongside the treaty itself, so the whole program is negotiated as one picture.
Ceding Commission: The Price of the Capacity
The reinsurer does not keep the ceded premium for free. On both treaty types it pays the cedent a ceding commission — a percentage of ceded premium reimbursing acquisition costs like brokerage and underwriting expense. If a quota share cedes $10,000 of premium at a 30% ceding commission, $3,000 comes straight back to the cedent.
Quota share commissions are often the centerpiece of the negotiation: because the reinsurer takes a slice of every risk including the small profitable ones, cedents push for higher flat commissions and frequently secure sliding-scale commissions that rise when the loss ratio beats target. Surplus treaty commissions are typically lower or flatter, because the cedent already keeps 100% of the premium on its retained share of every risk and cedes nothing below the retention — the reinsurer is paying for peak capacity on the larger lines, so the commission reflects that narrower role.
Frequently Asked Questions
What is a quota share treaty in one paragraph?
A quota share treaty is a proportional reinsurance agreement in which the cedent cedes a fixed percentage of every risk it writes — a 50% quota share means the reinsurer takes half of every premium and pays half of every loss, from the smallest homeowners line to the largest commercial account. The percentage never moves with risk size, so the split is perfectly predictable: the cedent knows exactly what it keeps and what it gives up before a single policy is written. In exchange for that premium, the reinsurer typically pays a ceding commission that reimburses the cedent’s acquisition costs.
What do surplus “lines” mean on a treaty slip?
A “line” is simply one multiple of the cedent’s retention. If the retention is $200,000, then one line equals $200,000, and a “9-line surplus treaty” gives the cedent nine of those multiples — $1.8 million of automatic reinsurance capacity above its own $200,000 retention. Each risk draws down only what it needs: the portion above the retention is measured in lines (whole or fractional) and ceded, while the retention itself always stays with the cedent. Risks at or below the retention use zero lines and are fully retained.
Can you walk through a worked example of a $1M line on a 9-line surplus treaty?
Take a $200,000 retention with a 9-line surplus treaty, and a $1,000,000 risk. The risk equals five lines in total: the cedent keeps the first line — its $200,000 retention, or 20% — and cedes the remaining four lines, $800,000, or 80%, to the reinsurer. Premium splits the same way, so 80% follows the $800,000 to the reinsurer. If the risk then suffers a $600,000 loss, the cedent pays $120,000 (20%) and the reinsurer pays $480,000 (80%) — the loss follows the exact same 20/80 division as the sum insured.
Why would a cedent choose a surplus treaty over a quota share?
A surplus treaty lets the cedent keep the economics of small risks while buying real capacity for large ones. Under a 50% quota share, a profitable $150,000 risk still hands half its premium — and half of every small loss — to the reinsurer, diluting the cedent’s best business. Under a surplus treaty with a $200,000 retention, that same $150,000 risk is fully retained: no premium ceded, no reinsurer involvement at all. The price is administration — every risk must be scheduled and measured in lines — but cedents with a spread of risk sizes often find surplus treaties cheaper in premium terms and kinder to retained profits.
What happens to lines above the treaty limit?
They fall outside the treaty entirely. A $3,000,000 risk on a 9-line surplus treaty with a $200,000 retention can only place nine lines — $1,800,000 — with the treaty reinsurer; capacity stops there. The remaining $1,000,000 must be placed facultatively with another reinsurer or retained outright by the cedent. In practice the broker arranges facultative cover before binding, so no part of the line is left unprotected — but the surplus treaty itself contributes nothing beyond its nine lines.
How do ceding commissions differ between quota share and surplus share?
Both treaty types pay a ceding commission — a percentage of the ceded premium that reimburses the cedent’s acquisition and administrative costs — but the economics sit in different places. Quota share commissions are often the larger negotiation lever: because the reinsurer takes a slice of everything, including small profitable risks, commissions are frequently flat percentages of ceded premium and sometimes slide with the loss ratio, rising when results are good. Surplus treaty commissions tend to be lower or flatter, because the cedent already keeps 100% of the premium on its retained share of every risk and gives up nothing below the retention — the reinsurer is being paid mostly for capacity on the larger lines.