Surplus belongs to the same family as quota share, the proportional family, and it corrects its main defect. Under a quota share the cedant cedes the same fraction of its smallest and its largest risk, which is absurd: it needed no help at all on the first. Surplus makes the cession rate vary, risk by risk, so that the cedant keeps everything it can carry and cedes only what exceeds.
The mechanism rests on a unit of measure, the line or retained line. The cedant sets the amount it accepts to keep on one risk, say 2 million euros, and that is its line. The treaty then grants it a number of lines, say nine, giving a total capacity of ten lines, that is 20 million: one line for itself, nine for the reinsurer. A 20 million risk is therefore ceded at 90%, a 4 million risk at 50%, and a 1.5 million risk is not ceded at all since it fits entirely within the line.
Once that rate is computed for a given risk, everything else follows proportionally, exactly as under a quota share: premium splits in that proportion and so do losses, whatever their size. This is where intuition most often trips. A 300,000 euro loss on a risk ceded at 90% produces a recovery of 270,000 euros, even though the cedant could perfectly well have absorbed 300,000 alone. The treaty does not look at the loss, it looks at the risk the loss came from.
The table of lines is the instrument that makes this workable. Rather than a single line, the cedant declares several, graded by the quality of the risk: a high line on a recent, protected, well-rated building, a reduced line on older construction or a difficult trade. The table is attached to the treaty and it is one of the documents the reinsurer scrutinizes most, because it describes exactly the underwriting discipline it is funding. A table that is too generous at the bottom end is a polite way of ceding bad risks more than good ones.
That is where adverse selection plays out, which is the real subject of this structure and what separates it from quota share. Under a quota share the cedant chooses nothing; under a surplus it chooses on every submission, by setting the applicable line. A surplus reinsurer therefore always buys two things at once: a portfolio, and the judgment of whoever decides the split. The clauses that frame that freedom, the definition of the unit of risk, the obligation to cede homogeneously, the ban on amending the table mid-year, are not paperwork.
The definition of the unit of risk deserves its own paragraph, because it decides the capacity actually available. Do two neighboring warehouses separated by a fire wall make one risk or two? If two, each consumes its own set of lines and capacity doubles; if one, a single set covers the whole. The treaty settles it by a rule, usually built on physical separation and on whether one loss can reach both, and that rule matters more to the cedant than the number of lines granted.
Surplus is finally very often combined with a quota share placed ahead of it, and the order matters. A 20% quota share applied first, then a surplus on the balance, does not give the same result as a surplus followed by a quota share on the retention. The first structure reduces the base the lines apply to, therefore peak capacity; the second leaves capacity intact and only lightens the retention. A reinsurance program is always read in its order of application, never as a list of treaties.
At January 1, 2026, a commercial insurer places a nine-line surplus on a retained line of 2 million euros for first-category risks. On June 4, a fire partly destroys a warehouse insured for 16 million, rated first category, and the damage comes to 1.2 million euros. The claims manager takes the view that no recovery is due, the loss being below the retained line. Is that right?
The claims manager is applying non-proportional logic to a proportional treaty, and that is the most common confusion about this structure. A surplus never compares the loss to the retention: it compares the SUM INSURED to the line, once, at the moment the risk enters the treaty. Here the sum insured is 16 million against a 2 million line, so the cedant keeps 2 out of 16, that is 12.5%, and cedes 14 million, that is 87.5%. That 87.5% is fixed for this risk and for the whole of its cover. It then applies to the premium, and it applies in the same way to any loss, whatever its size. The 1.2 million damage therefore produces a recovery of 87.5% of 1.2 million, that is 1,050,000 euros, and the cedant keeps 150,000. Two checks remain before notifying. It must be confirmed that the warehouse is indeed a single unit of risk within the treaty's meaning, because if it is split into two fire-walled buildings the sum insured to hold is not 16 million and the rate changes. And it must be checked that the risk was rated first category in the table of lines at inception, and not reclassified since, the table not being amendable mid-year.
- 01Surplus makes the cession rate vary risk by risk: the cedant keeps what it can carry and cedes only the excess.
- 02The rate is computed by comparing the sum insured to the line, never the loss to the retention.
- 03Once the rate is set for a risk, it applies to the premium and to all of its losses, small ones included.
- 04The table of lines describes the underwriting discipline the reinsurer is funding: it is the most scrutinized document in the placement.
- 05The definition of the unit of risk decides the capacity actually available, often more than the number of lines granted.
- 06A program is read in its order of application: quota share before or after surplus does not give the same result.