STM Deductible Math: Why the Cheapest Plan Can Cost You the Most
The $9,000 emergency room scenario
Say you land in the ER with a broken ankle and the total bill is $9,000. On Plan A ($100/month premium, $10,000 deductible, 100% coinsurance after) you pay everything: $9,000 out of pocket. On Plan B ($180/month, $2,500 deductible, 80/20 coinsurance, $8,000 out-of-pocket max) you pay $2,500 + 20% of the remaining $6,500 ($1,300) = $3,800. Plan B costs $960 more per year in premium but saves you $5,200 on this single claim.
The break-even trick
The rule of thumb: compare plans by premium + worst-case out-of-pocket, not premium alone. Add twelve months of premium to the plan’s out-of-pocket maximum. The lowest total is the plan that protects you best if the year goes badly — and STM exists precisely for the year that goes badly.
| Plan | Monthly | Deductible | Annual premium | Worst-case year total |
|---|---|---|---|---|
| Plan A | $100 | $10,000 | $9,600 | $10,600 |
| Plan B | $180 | $2,500 | $2,160 | $4,660 |
| Plan C | $240 | $1,000 | $2,880 | $3,880 |
FAQ
Are deductibles per person or per family?
On individual STM they are per person; family plans usually embed individual deductibles at 2-3 members.
Do fixed-cash benefits count toward the deductible?
No — they are paid in addition to the coinsurance schedule.
Can I change my deductible mid-term?
Rarely. Most carriers lock the tier until the term ends; you re-apply at renewal.