Overview: The underwriting rules differ fundamentally between individual and group coverage, with important implications for enrollment timing and risk pricing.

Medical Underwriting

In the individual market, ACA-compliant plans are fully guaranteed issue with no medical underwriting. In the non-ACA individual market (short-term plans, Medigap outside guaranteed-issue windows, supplemental products), traditional medical underwriting — including health questions, medical exams, and risk classification — applies fully.

In the group market, employees are not individually underwritten regardless of plan size. An employer cannot charge different premiums to employees based on health status, and employees cannot be denied coverage. For large groups, the employer's premium is set based on the group's collective experience (experience rating). For small groups, community rating rules similar to the individual market apply.

Enrollment Periods

Individual market: Enrollment is limited to the annual Open Enrollment Period (typically November 1 through January 15 for most states) and Special Enrollment Periods (triggered by qualifying life events like losing other coverage, marriage, birth of a child, or relocation). The window for a SEP is usually 60 days from the qualifying event.

Group market: New employees can typically enroll when first eligible (subject to a waiting period of up to 90 days). Annual open enrollment is employer-defined. Mid-year enrollment is permitted for qualifying life events, but the SEP window in group plans is typically 30 days from the event — shorter than the individual market.

Feature	Individual (ACA)	Group
Medical underwriting	Prohibited	Not used for individual employees
Basis for group premium	Community rating (4 factors only)	Experience rating (large groups)
Annual enrollment	Nov 1–Jan 15 (approx.)	Employer-set date
Mid-year SEP window	60 days from qualifying event	30 days from qualifying event
New entrant enrollment	Requires qualifying event	Upon hire (up to 90-day wait)