medical trend
If you ran a health plan and charged the same premium next year as this year, you would lose money — not because you did anything wrong, but because health care simply costs more each year. A doctor visit, a hospital day, a brand-name drug all tend to get pricier, and people also tend to use more of them. Medical trend is the name for this year-over-year growth in the cost of health claims, and projecting it is one of a health actuary's most consequential jobs.
Crucially, medical trend is more than ordinary inflation. It has two engines: unit price (the cost of each service rising) and utilization (people using more services, new treatments appearing, providers ordering more). It can also be pushed by 'mix' shifts toward more expensive technology and by leveraging — because a fixed deductible covers a smaller fraction of a bigger bill over time, the insurer's share grows faster than the total. A 6% headline trend might be, say, 3% price plus 3% utilization. If claim cost is 1,000 PMPM today and trend is 7%, next year's projection is 1,000 x 1.07 = 1,070 PMPM.
Trend drives almost every health number that looks forward: next year's premium, the rate increase filed with regulators, and the reserves for claims not yet paid. It is also genuinely uncertain — it shifts with new drugs, epidemics, policy changes, and the economy — so actuaries study it constantly, split it by service category, and treat a wrong trend assumption as one of the biggest risks in health pricing. Underestimate trend and the plan loses money; overestimate it and the plan prices itself out of the market.
Last year a plan paid 5,000 in claims per member. The actuary expects 4% from unit price increases and 3% from rising utilization, for a combined trend of about 7.1% (1.04 x 1.03). Projected claim cost next year is 5,000 x 1.071 = 5,355 per member — and the premium must rise roughly in step, or the plan runs at a loss.
Trend = price growth x utilization growth; it compounds year on year.
Medical trend is usually well above general consumer inflation, and it compounds — a few percentage points wrong, repeated over several years, becomes a large pricing error. It is not a fixed constant; it must be re-estimated and split into its drivers each cycle.