Two surveys published within a week of each other are putting the same number on the table. Business Group on Health (BGH) released its 2027 Large Employers’ Health Care Strategy and Plan Design Survey on August 25, projecting a median health cost trend of 9.2% before plan design changes. Mercer followed on August 31 with preliminary results from its 2026 National Survey of Employer-Sponsored Health Plans, pegging average 2027 trend at 8.2% after cost-management actions. According to Mercer, that 8.2% is the highest projected increase since 2003.
The simultaneous convergence of two independent surveys above 9% (gross trend) matters more than either number alone. Survey disagreement is normal; survey agreement at a 20-year high is a reserve signal.
Who It Affects
Self-insured plan sponsors renewing stop-loss coverage in fall 2026 for a January 1, 2027 effective date face the most immediate exposure. This includes corporate self-funded plans, hospital health plans, public-entity benefit programs, and group captives covering employee health. The urgency is structural: the aggregate stop-loss attachment negotiated during open enrollment is locked in for the full 2027 plan year. There is no mid-year adjustment mechanism without a plan amendment or a rider that most carriers will not grant retroactively.
Plans that accepted their stop-loss carrier’s proposed aggregate without independently verifying the trend assumption embedded in that proposal are carrying unhedged retained risk they may not have quantified.
The Reserve Mechanism: Aggregate Attachment Math
Aggregate stop-loss covers the self-insured plan’s total annual claims above a corridor threshold, typically set at 110% to 125% of expected annual claims. “Expected” is the operative word. The attachment is calculated by taking prior-year actual claims, applying an agreed trend factor, and multiplying by the corridor percentage.
If the stop-loss carrier priced the 2027 aggregate using a 5% to 6% trend assumption — consistent with what mid-market carrier proposals were quoting in fall 2025 — and actual trend runs at 9.2%, the attachment point is understated by approximately 3 to 4 percentage points of expected annual claims.
The dollar consequence is direct. For a self-insured plan with $5 million in prior-year claims, a 6% trend assumption produces expected 2027 claims of $5.3 million. Set the aggregate attachment at 110%, and the corridor threshold sits at $5.83 million. The same plan with 9.2% trend has expected claims of $5.46 million; the correct 110% corridor sits at $6.01 million. The gap between those two thresholds — $180,000 — is unhedged retained risk. The plan bears that corridor in full; the stop-loss carrier does not.
For larger plans, the numbers scale proportionally. A $20 million plan with the same trend gap carries approximately $720,000 of unhedged corridor exposure.
Where This Shows Up in Your Reserves
For self-insured plans carrying quarterly IBNR accruals, the trend gap has a second-order effect. Incurred-but-not-reported (IBNR) reserves for health plans are typically estimated by projecting ultimate claims from paid-to-date experience, using a completion factor derived from historical runout speed and an assumed trend. If the trend loaded into that projection was set in early 2026 using a 5% to 7% assumption, then Q3 2026 IBNR is understated by the same proportional gap on claims not yet reported.
Self-funded plans that finalize their December 31, 2026 balance sheet accrual in January or February 2027 should expect upward pressure on unpaid claim liability if they have not already adjusted for the 9.2% gross trend.
The BGH survey also flags two cost drivers that are particularly difficult to model from historical data. Hospital price increases were cited by 62% of surveyed employers as a major 2027 cost driver; outpatient facility costs, by 48%. Hospital pricing is the category least visible to self-insured plan sponsors through standard network discounting and the hardest to capture in an IBNR run-out built from plan administrator data, which typically lags facility contract changes by one to two quarters.
Pharmacy adds a separate layer: pharmacy now represents 25% of total employer health expenditure, and employer drug costs are projected to rise 12% in 2027. GLP-1 weight-loss medications were cited by 68% of BGH survey employers as an emerging cost pressure, with 14% of respondents planning to drop GLP-1 coverage. Plans retaining GLP-1 coverage will absorb utilization shifting from those that drop it, a dynamic that does not appear in any trailing-period data used to fit completion factors or development patterns.
Mercer estimates that GLP-1 utilization alone accounts for approximately one percentage point of the projected 8.2% average 2027 trend increase.
What This Means for Your Next Review
Any self-insured plan sponsor whose stop-loss renewal is currently in negotiation should ask the stop-loss carrier or TPA to show the trend assumption embedded in the proposed aggregate attachment. If that assumption is below 8%, the corridor is being priced on a stale number. The aggregate percentage itself (110% versus 115% versus 125%) is a secondary question; the trend embedded in “expected claims” is the variable that determines whether the attachment sits where it should.
For plans where the 2027 stop-loss renewal is already signed, the question is whether the aggregate attachment was set with an accurate trend. If it was not, the CFO and risk manager need to know the unhedged dollar exposure before Q4 begins, not after the first corridor breach.
Decision-Maker Checklist
- Ask your stop-loss carrier or broker to state the trend assumption used to calculate the 2027 aggregate attachment, in writing.
- Compare that stated trend to the BGH 9.2% gross and 8% net figures; quantify the dollar gap in corridor exposure for your plan size.
- Confirm that your Q3 2026 IBNR accrual uses a trend assumption of at least 8%; if it was set in early 2026 using historical runout without a trend update, ask your TPA or consulting actuary to restate it.
- Identify the share of your covered population using GLP-1 medications and ask whether a separate loading factor has been applied to expected pharmacy claims.
- For group captive participants: confirm that the captive’s aggregate corridor for the health benefit layer was reset for 2027 using current trend, not prior-year assumptions carried forward from a lower-trend environment.
- Put trend assumption verification on the agenda for your next stop-loss renewal meeting, and request that the carrier document the methodology in the proposal rather than embedding it in a black-box expected-claims figure.
An independent reserve review brings a second pair of eyes that is free of the TPA’s or fronting carrier’s incentive structure. We are working on a directory of independent reviewing actuaries. If you would like to be considered, get in touch.
Sources
- Business Group on Health: 2027 Large Employers’ Health Care Strategy and Plan Design Survey press release, August 25, 2026
- Mercer / Marsh: 2026 National Survey of Employer-Sponsored Health Plans preliminary results, via Business Wire, August 31, 2026
- Mercer insight: “Survey: Health benefit costs expected to jump 8.2% in 2027, the biggest increase since 2003”
- MedCity News: BGH survey coverage, August 25, 2026
- Stop-Loss Reinsurance at 15% Signals a Multi-Year Rate Floor
- Segal Q3 2026: Stop-Loss $1M Claims Growing 25 Percent per Year
- IBNR for Self-Funded Health Plans