What it means
A company that self-insures routine losses accepts a predictable annual cost in exchange for a much lower premium. What it cannot accept is an abnormal year where frequency or severity runs far above plan.
Aggregate excess insurance solves exactly that problem by covering the aggregate outcome rather than individual events. Two numbers define the cover.
The attachment point is the total loss figure at which the insurer's obligation starts, and the limit is the most the insurer will pay above that point. Losses above the attachment point plus the limit fall back on the business, which is why the limit deserves as much attention as the attachment.
Attachment points are usually set as a percentage of expected losses, commonly somewhere between 110% and 150% of the actuarially expected figure. Setting it too low makes the premium expensive and defeats the purpose of self-insuring; setting it too high leaves the business exposed to the very scenario it was trying to insure against.
The cover is normally written alongside specific excess insurance, which responds to any single claim above a per-claim threshold. Together they protect against the two ways a self-insured programme can go wrong: one enormous claim, or a great many ordinary ones.
Buying only one of the two leaves an obvious hole. The practical nuance is definitional.
Policies differ on whether claims are counted when incurred or when paid, whether they must be reported inside the period, and whether claims already recovered under specific excess cover still count towards the aggregate. Those clauses decide whether a claim year actually reaches the attachment point.
In practice
Real-world examples.
Example
A staffing agency with 4,000 workers on assignment self-insures workers compensation up to $1,500,000 a year and buys aggregate excess above it. A hard winter produces an unusual cluster of slip injuries, total losses reach $1,950,000, and the insurer funds the $450,000 above the attachment point.
Example
A grocery chain sets its attachment point at 130% of expected losses because its claims history has been extremely stable. Its broker warns that a single product recall could still blow through the layer, so the chain buys a separate specific excess policy for individual events.
Example
A haulage operator finds its aggregate excess policy counts only claims reported within the policy year. Two late-reported incidents from the prior year push the current total higher but are excluded from the count, and the group ends the year $180,000 short of its attachment point despite feeling like it had a terrible year.
Formula
Calculation
Insurer recovery = total covered losses - attachment point, capped at the policy limit and floored at zero, and the insured retains everything else.
A construction group self-insures its liability exposures with an aggregate excess policy attaching at $2,000,000 and providing a limit of $3,000,000, so the insurer covers the layer from $2,000,000 up to $5,000,000.
In a normal year the group records total covered losses of $2,750,000. Recovery is $2,750,000 - $2,000,000 = $750,000, the insurer pays that amount, and the group retains the $2,000,000 attachment layer.
Now take a severe year with total covered losses of $6,000,000. The calculated recovery would be $6,000,000 - $2,000,000 = $4,000,000, but the limit caps the payment at $3,000,000. The group therefore retains $2,000,000 below the attachment point plus $6,000,000 - $5,000,000 = $1,000,000 above the top of the layer, a total retention of $2,000,000 + $1,000,000 = $3,000,000. That gap is exactly why buyers stress-test the limit as hard as the attachment.Case study
Seen in the real world.
Ironbridge Scaffolding is an illustrative, fictional access equipment contractor that had self-insured its liability exposures for six years. Expected annual losses were around $1,600,000, and the company set its aggregate excess attachment point at $2,000,000 with a $3,000,000 limit, paying a premium of $265,000.
For five years the arrangement worked exactly as designed. Losses ranged from $1,340,000 to $1,810,000, never reaching the attachment point, and Ironbridge saved an estimated $600,000 a year against a fully insured programme.
In the sixth year a site collapse and two related injury claims took total losses to $4,400,000. The insurer paid $4,400,000 - $2,000,000 = $2,400,000, comfortably inside the $3,000,000 limit, and Ironbridge absorbed $2,000,000. In this fictional case the board's conclusion was that the structure had worked, but it raised the limit to $5,000,000 at renewal after modelling a scenario in which the same collapse had involved a second crew.
Watch out
Common mistakes.
- Focusing entirely on the attachment point and treating the limit as a formality. Losses above the top of the layer come straight back to the business, and that is where genuine solvency risk sits.
- Assuming aggregate excess cover responds to a single catastrophic claim. It responds to the annual total, so a company also needs specific excess cover for individual large events.
- Setting the attachment point from last year's losses alone. A single year is a poor guide, and attachment points should be based on several years of data adjusted for changes in exposure.
Questions
People also ask.
What is the difference between aggregate excess and specific excess insurance?
Aggregate excess responds when total annual losses pass a threshold, while specific excess responds when any one claim passes a threshold.
How is the attachment point usually set?
As a multiple of expected losses, most often between 110% and 150%, so that the cover responds only in a genuinely abnormal year.
Is aggregate excess insurance the same as stop-loss cover?
They work on the same principle, and the term stop-loss is generally used when the underlying programme is a self-funded employee benefits plan.
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