Short answer: Everyone in a class must get the same terms, but the allowance may go up with age (the oldest no more than three times the youngest) and with the number of covered dependents, as long as the same schedule applies to everyone in the class. Different classes can get different amounts.
Design rules for an ICHRA (CHOICE Arrangement) from 26 CFR 54.9802-4(c)(3):
- Age. An age-based schedule is allowed if the oldest participant’s maximum is no more than 3 times the youngest’s, and the method of determining age is set before the plan year and used for everyone in the class.
- Family size. The amount may rise with the number of covered dependents if everyone with the same number of dependents gets the same amount.
- Carryover. Unused amounts may roll into later years if the carryover method is the same for the whole class.
- Section 125. If any employee in the class can pay the rest of an off-Marketplace premium pre-tax, everyone in the class must have the same option.
A practical starting point is the individual premiums employees will actually face. Individual premiums rise with age, so an age-based allowance keeps older employees from being priced out while holding down cost for younger ones. Then check affordability for each employee: it depends on age and home rating area, so one flat amount can be affordable for one employee and unaffordable for the person at the next desk.