The Annual Open Enrollment Calendar: Key Dates You Need to Know

Why Open Enrollment Dates Matter More Than You Think

Most people treat open enrollment as an annual reminder they can deal with later — and then later arrives too fast. Missing your enrollment window isn't just inconvenient. Depending on which program you're in, it can mean going without coverage for months, paying out-of-pocket for care, or being locked into a plan that no longer fits your life.

Open enrollment works differently depending on whether your coverage comes from an employer, the ACA marketplace, or Medicare. Each program runs on its own calendar with its own rules. This guide gives you the exact dates, grouped by program, so you know precisely when to act — and what happens if you don't.

Think of this as your annual insurance calendar. Bookmark it, set phone reminders, and share it with a family member who also needs to enroll. The few minutes you spend now will protect you from scrambling when deadlines arrive.

ACA Marketplace Open Enrollment: Federal and State Dates

The ACA marketplace — sometimes called the health insurance exchange — runs a federally defined open enrollment period each fall. Here's how it works for the federal marketplace at HealthCare.gov:

• Opens: November 1
• Deadline for January 1 coverage: December 15
• Final deadline (February 1 coverage): January 15

What that means in plain terms: if you complete your enrollment by December 15, your coverage starts January 1. If you miss that but enroll between December 16 and January 15, your coverage starts February 1 instead — leaving you without coverage for the first month of the year.

If you live in a state that runs its own exchange — such as California (Covered California), New York (NY State of Health), or Massachusetts (Health Connector) — your dates may be different. Many state exchanges extend their final deadline into late January or even mid-February. Check your state exchange directly rather than assuming the federal dates apply to you.

To learn more about how the marketplace enrollment process works, see our guide on how the ACA open enrollment window operates, including what you can and cannot do once the window closes.

If you miss the ACA window entirely, your only path to coverage is a qualifying life event that triggers a Special Enrollment Period. Examples include losing job-based coverage, getting married, having a baby, or moving to a new coverage area. Without one of these, you'll need to wait until the next open enrollment season.

Medicare Enrollment Windows: Three Separate Periods to Know

Medicare operates on a different calendar from the ACA marketplace, and it actually has three distinct enrollment periods — each with a different purpose. Confusing them is one of the most common mistakes I see people make, especially those transitioning from employer coverage at age 65.

1. Medicare Annual Enrollment Period (AEP)

• Dates: October 15 – December 7
• Coverage effective: January 1 of the following year
• Who it's for: Anyone already enrolled in Medicare who wants to switch plans
• What you can do: Switch from Original Medicare to Medicare Advantage (or vice versa), change your Medicare Advantage plan, or add/change a Part D prescription drug plan

2. Medicare Advantage Open Enrollment Period (MA OEP)

• Dates: January 1 – March 31
• Coverage effective: First day of the month after you enroll
• Who it's for: People already enrolled in a Medicare Advantage plan
• What you can do: Switch to a different Medicare Advantage plan, or drop Medicare Advantage and return to Original Medicare (with or without a Part D plan)
• What you cannot do: Switch from Original Medicare to Medicare Advantage — that requires either the AEP or a Special Enrollment Period

3. Initial Enrollment Period (IEP)

• Dates: A 7-month window — begins 3 months before the month you turn 65, includes your birth month, and extends 3 months after
• Coverage effective: Varies based on when within your IEP you enroll
• Who it's for: People becoming eligible for Medicare for the first time

For a direct comparison of how Medicare enrollment differs from ACA marketplace enrollment, see our side-by-side breakdown: Medicare vs. ACA open enrollment compared.

Employer-Sponsored Plans: What Your HR Department Controls

If you get insurance through your job, your open enrollment window is set entirely by your employer — not by the federal government. There is no universal start date. Most large employers run open enrollment in October or November for a January 1 plan year start, but this varies significantly.

Here's what typically happens during employer open enrollment:

1. Your HR team or benefits administrator announces open enrollment — usually via email, the HR portal, or a mailed benefits guide. Watch for this communication carefully; it's easy to miss.
2. A window opens, typically lasting 2–4 weeks, during which you can add or drop coverage, change plan types (e.g., from a PPO to an HDHP), add or remove dependents, and enroll in FSAs or HSAs.
3. If you do nothing, you may be auto-re-enrolled in your current plan — but this isn't guaranteed, and your costs or plan details may have changed significantly.
4. The window closes, and your elections are locked in for the plan year.

A few important nuances for employer plans:

• Companies with non-calendar fiscal years may run open enrollment at a completely different time of year (e.g., June for a July 1 plan year).
• If your employer switches insurance carriers, you may be required to actively re-enroll even if you were previously auto-renewed.
• Life events like marriage, divorce, or the birth of a child allow you to make mid-year changes outside of open enrollment under HIPAA Special Enrollment rules — not the ACA SEP rules, though the triggers are similar.

Before your employer's window closes, use our open enrollment checklist to make sure you've reviewed every decision — not just health insurance, but dental, vision, life insurance, disability, and FSA/HSA contributions.

Medicaid, CHIP, and Programs Without Enrollment Windows

Not every insurance program runs on an annual open enrollment cycle. Medicaid and the Children's Health Insurance Program (CHIP) accept applications year-round. If you qualify — based on income, household size, age, disability, or other criteria — you can apply any time and coverage can begin within days to weeks of approval.

This is an important safety net to know about. If you lose your job mid-year and your income drops, you may suddenly qualify for Medicaid even if you've never been eligible before. You don't have to wait for November.

Other programs without fixed annual enrollment windows include:

• Medicare Savings Programs — Help with Medicare premiums and cost-sharing for low-income beneficiaries; available year-round through your state Medicaid agency
• Extra Help / Low Income Subsidy (LIS) — Reduces Part D prescription drug costs for Medicare beneficiaries; apply any time through Social Security
• TRICARE — Military health coverage that generally does not use an annual open enrollment window for most eligible beneficiaries

If you're unsure whether you qualify for Medicaid or a subsidy on the ACA marketplace, the ACA marketplace plan tools can screen your eligibility when you create an account — even outside of open enrollment.

Your Year-Round Open Enrollment Action Plan

Even though the actual enrollment windows are concentrated in fall and winter, the preparation should start earlier. Here's a month-by-month framework I recommend to clients every year:

August – September: Gather and Review

• Pull your Explanation of Benefits (EOB) statements from the past year — note which services you used and how much you paid out-of-pocket
• Make a list of all prescriptions you take regularly and check if your current plan's formulary still covers them
• Confirm that your primary care doctor and any specialists are still in-network under your current plan
• Estimate next year's expected healthcare needs: upcoming surgeries, pregnancies, therapy, or chronic condition management

October: Watch for Enrollment Materials

• Monitor your mail and email for Medicare Annual Notice of Change (ANOC) letters if you're on Medicare — these arrive by September 30 and show changes to your plan for next year
• Watch for your employer's open enrollment announcement and benefits guide
• Check HealthCare.gov or your state exchange for any plan or premium changes for next year (previews are often available before November 1)

November – December: Enroll and Confirm

• Complete enrollment by December 15 if you want January 1 ACA marketplace coverage
• Complete Medicare plan changes by December 7
• Submit employer plan elections before your HR deadline
• Apply for Medicaid any time if your income qualifies — don't wait
• Confirm your enrollment in writing: save confirmation numbers, take screenshots, and watch for your new insurance card

January – March: Verify and Adjust

• Verify that your new ID card arrived and matches your elected plan
• Confirm your first premium payment was processed
• If you're in Medicare Advantage and want to make a change, you still have until March 31 during the MA Open Enrollment Period

For a full step-by-step checklist tailored to ACA marketplace enrollment specifically, see the ACA enrollment season checklist. And if you want the big picture — how all these pieces fit together — the complete open enrollment guide covers every aspect from plan types to subsidies to common mistakes.