Deadlines to Know for 2025 Health Insurance Enrollment

Every fall in the U.S., two big health insurance enrollment windows open. One is for people who buy coverage through the Affordable Care Act (ACA) Marketplace, and the other is for people on Medicare. They overlap on the calendar, but they serve different audiences and have different rules. Miss either one, and you could find yourself locked into a plan that doesn’t fit, or worse, without coverage altogether. Here’s what you need to know about the 2025 deadlines, how the two enrollment periods compare, and what happens if you miss them.

Marketplace Open Enrollment (ACA)

If you’re not yet 65, or you don’t have employer health insurance, chances are you rely on the ACA Marketplace (Healthcare.gov or your state’s exchange). This is the annual window when you can sign up for a new plan, switch plans, or renew coverage for the following year.

• When it runs: 
  • November 1, 2025 – January 15, 2026 in most states. 
  • A handful of state-run marketplaces, such as California, New Jersey, New York, Rhode Island, and Washington, D.C., run slightly longer (through January 31). 
• Key cutoff dates: 
  • December 15, 2025: Enroll by this date if you want your new coverage to start on January 1, 2026. 
  • January 15, 2026: Final day to apply for 2026 coverage in most states. If you enroll between Dec. 16 and Jan. 15, your plan will start February 1, 2026. 
• Automatic renewal: 
  • If you don’t do anything, the Marketplace may automatically re-enroll you in your current plan or a “similar” plan chosen by the exchange. That can be convenient, but it’s risky: your network or premiums could change, so it’s best to log in and confirm. 
• What if you miss it? 
  • Outside the enrollment window, you can only sign up if you qualify for a Special Enrollment Period (SEP). SEPs are triggered by major life events like losing other coverage, moving, getting married or divorced, or having a child. You usually get 60 days from the event to act.
    

Medicare Annual Enrollment Period (AEP)

If you’re 65 or older, or otherwise enrolled in Medicare, your annual window is different: the Medicare Annual Enrollment Period (AEP).

• When it runs: 
  • October 15 – December 7, 2025. 
• What you can do: 
  • Switch from Original Medicare (Parts A & B) to a Medicare Advantage plan (Part C). 
  • Switch back from Medicare Advantage to Original Medicare. 
  • Move from one Medicare Advantage plan to another. 
  • Join, switch, or drop a Part D prescription drug plan. 
• When changes take effect: 
  • All changes made during AEP begin January 1, 2026. 
• Why it matters: 
  • Medicare Advantage and Part D plans change every year. Formularies (drug lists), provider networks, and monthly premiums can all shift. If you do nothing, you’ll stay in your current plan, but it may not fit your medical or financial needs the same way next year.
    

Private Health Insurance (PHI) Outside ACA and Medicare

Not everyone goes through the ACA Marketplace or Medicare. Some people purchase private health insurance (PHI) directly from an insurer or broker, sometimes called “off-exchange” coverage.

• Enrollment timing: 
  • Similar to the ACA, most private insurers follow the same November–January enrollment calendar for individual/family plans, since they are legally required to align with ACA rules. 
  • However, some short-term health plans or non-ACA-compliant products can be purchased year-round. 
• If you miss ACA or Medicare deadlines: 
  • PHI may give you options, but be cautious: plans sold outside the ACA may not cover essential benefits, may cap coverage, or may exclude preexisting conditions. 
  • True “major medical” private insurance usually can’t be purchased outside open enrollment unless you qualify for a Special Enrollment Period, just like ACA plans. 
• Deadlines to note: 
  • If you’re buying directly from an insurer (off-exchange), the same Dec. 15 cutoff typically applies for Jan. 1 coverage, and the Jan. 15 cutoff applies for Feb. 1 coverage.
    

How OEP, AEP, and PHI Overlap

• ACA OEP: Nov. 1 – Jan. 15 (most states); coverage starts Jan. 1 or Feb. 1 depending on when you enroll. 
• Medicare AEP: Oct. 15 – Dec. 7; changes always start Jan. 1. 
• PHI: Generally follows ACA timelines for major medical, but some short-term and limited-benefit policies are available year-round.
  

Employer Coverage, Medicaid, and CHIP

Not everyone fits neatly into ACA, Medicare, or PHI.

• Employer plans: Most employer-sponsored plans hold their own open enrollment windows in October or November. The dates vary by employer but usually last 2–4 weeks. 
• Medicaid and CHIP: Enrollment is year-round in most states if you meet eligibility rules. No narrow window applies.
  

Key Dates at a Glance

• Medicare AEP: Oct. 15 – Dec. 7, 2025 (changes effective Jan. 1, 2026). 
• ACA OEP (federal): Nov. 1, 2025 – Jan. 15, 2026. 
  • Dec. 15 = Jan. 1 coverage start. 
  • Dec. 16 – Jan. 15 = Feb. 1 coverage start. 
• State-run marketplaces: Some extend through Jan. 31, 2026. 
• Private health insurance (off-exchange): Usually mirrors ACA deadlines; short-term or limited plans can be purchased year-round. 
• Employer open enrollment: Usually Oct.–Nov. 2025 (varies). 
• Medicaid/CHIP: Year-round if eligible.
  

Bottom Line

The fall of 2025 is when health insurance decisions get made for the year ahead. If you’re on Medicare, your critical window is Oct. 15 – Dec. 7. If you’re shopping on the ACA Marketplace or directly through an insurer, your main window is Nov. 1 – Jan. 15, with Dec. 15 as the most important cutoff for Jan. 1 coverage.

Miss those dates, and your options narrow quickly. Special Enrollment Periods may save you, and some short-term private plans may be available, but they rarely offer the full protections of ACA or Medicare. The safest move is to mark your calendar, review your choices carefully, and lock in coverage before the deadline passes.