What it means
When an employer self-funds a health plan, it pays each medical claim from its own money instead of paying a fixed premium to an insurer. That usually costs less, because the employer is not paying an insurer's risk margin, but it leaves the company exposed to whatever the year happens to produce.
Aggregate stop-loss cover puts a ceiling on that exposure. The attachment point is set as a percentage of expected annual claims, most commonly 120% to 125%.
Expected claims come from an actuarial estimate based on the size and profile of the workforce, and the corridor between expected claims and the attachment point is the amount of bad luck the employer agrees to absorb before help arrives. Aggregate cover is almost always paired with specific stop-loss, which reimburses any individual member's claims above a per-person threshold.
Specific cover handles one very sick employee; aggregate cover handles a year where a great many employees are moderately unwell. Most claims that trigger specific cover are excluded from the aggregate calculation, which is a detail that materially changes the numbers.
The contract terms deserve careful reading. Policies specify which claims count, usually by whether they were incurred and paid within defined windows, and a mismatch between those windows can leave claims uncovered at the start or end of a contract.
Aggregating specifications also state a minimum attachment point so the insurer is never exposed to a low threshold if enrolment falls. Cash flow, again, is the practical issue.
Reimbursement typically arrives after the plan year ends unless the employer buys monthly accommodation, which advances funds during the year. Without it, the company can be paying claims for months before seeing a cent back.
In practice
Real-world examples.
Example
A regional accountancy firm with 180 staff moves from a fully insured plan to self-funding with a 125% aggregate stop-loss attachment. Claims come in at 96% of expected, so the firm keeps the difference rather than handing it to an insurer as retained premium.
Example
A food processor sees an unusual cluster of orthopaedic surgeries after a change in work patterns. Individual claims are too small to hit the specific stop-loss threshold, but the total reaches 118% of expected, and because the attachment point sits at 115% the aggregate policy reimburses the excess.
Example
A retail chain with seasonal headcount swings finds its aggregate attachment point recalculated monthly against actual enrolment. When headcount falls in the spring, the attachment point falls with it, which the finance team had not modelled in the annual budget.
Formula
Calculation
Attachment point = expected annual claims x attachment factor, and reimbursement = actual claims - attachment point, floored at zero and capped at the policy limit.
A manufacturer with 400 employees self-funds its health plan. The actuarial estimate of expected annual claims is $4,000,000, and the stop-loss carrier sets the attachment factor at 125%, so the attachment point is $4,000,000 x 1.25 = $5,000,000.
The plan year turns out badly and actual eligible claims reach $5,600,000. Reimbursement is $5,600,000 - $5,000,000 = $600,000, and the employer retains the $5,000,000 below the attachment point.
The aggregate stop-loss premium for the year was $180,000. Net benefit in this particular year is $600,000 - $180,000 = $420,000. It is worth noting that in a normal year with claims of, say, $4,100,000, the employer would receive nothing and the $180,000 premium would simply be the cost of knowing that $5,000,000 plus the premium was the worst the year could cost.Case study
Seen in the real world.
Halden Precision Tools is a fictional, illustrative engineering business with 520 employees that had been fully insured for years at an annual premium of $6,400,000. Its broker calculated expected claims of $5,100,000, suggesting roughly $1,300,000 a year was going to the insurer's margin and administration.
Halden moved to self-funding with a specific stop-loss threshold of $175,000 per member and an aggregate attachment factor of 125%, giving an attachment point of $5,100,000 x 1.25 = $6,375,000. Combined stop-loss premiums and administration came to $1,150,000, leaving a worst-case total cost of $6,375,000 + $1,150,000 = $7,525,000 against the previous fixed $6,400,000.
In year one, claims came in at $4,720,000, so total cost was $4,720,000 + $1,150,000 = $5,870,000, saving $530,000 against the old premium. In year two claims reached $6,900,000, but two members breached the specific threshold and $610,000 of their claims were removed from the aggregate calculation, leaving $6,290,000 of eligible claims, just under the attachment point. In this illustrative case Halden received no aggregate reimbursement and learned that the interaction between the two stop-loss layers, not the headline attachment percentage, decides what actually gets paid.
Watch out
Common mistakes.
- Assuming aggregate stop-loss covers a single catastrophic claim. That is the job of specific stop-loss cover, and buying only the aggregate leaves an obvious gap.
- Ignoring how claims already counted under specific stop-loss are treated. Many contracts strip those amounts out of the aggregate total, which can keep a bad year below the attachment point.
- Budgeting only the attachment point. The true worst case is the attachment point plus stop-loss premiums plus administration fees, and that is the number to compare with a fully insured quote.
Questions
People also ask.
What is a typical attachment factor?
Most contracts sit between 120% and 125% of expected claims, though larger employers with stable experience sometimes accept more.
When does the money actually arrive?
Often only after the plan year is settled, unless the employer pays for monthly accommodation, which advances reimbursements during the year.
Does self-funding with stop-loss always cost less?
No, it costs less on average across several years, but any single year can be more expensive, so it suits employers with the balance sheet to absorb variation.
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