Federal regulators have now locked in the Medicare and ACA Open Enrollment 2027 Dates after months of legal back and forth over how long Americans would actually get to shop for coverage. The Centers for Medicare and Medicaid Services confirmed in early August 2026 that Affordable Care Act enrollment for 2027 health plans will run from November 1, 2026 through January 15, 2027 on HealthCare.gov, after a federal judge struck down a rule that would have cut the window short at December 15. We’ll be updating this article monthly as CMS finalizes premium data and as state marketplaces confirm their own final schedules, so bookmark this page for the latest confirmed dates.

Medicare’s enrollment calendar, by contrast, is not in dispute this year. The Medicare Annual Enrollment Period keeps its long-standing schedule of October 15 through December 7, 2026, giving beneficiaries the usual seven-week window to compare Medicare Advantage and Part D drug plans for 2027. What makes this enrollment season unusually consequential is what is happening underneath these dates: enhanced Affordable Care Act subsidies that lowered premiums for millions of people expired at the end of 2025 and were never restored by Congress, and a separate federal subsidy that had been holding down Medicare drug plan premiums is also ending after 2026. This guide lays out the complete, confirmed calendar for both programs and explains exactly what has changed heading into 2027.

Medicare Annual Enrollment Period 2027: Key Dates

The Medicare Annual Enrollment Period (AEP), sometimes called the Medicare Open Enrollment Period, follows the same federally set schedule every year regardless of policy changes elsewhere in the healthcare system. For 2027 coverage, the window runs from October 15 through December 7, 2026. During this period, anyone with Medicare can switch from Original Medicare to a Medicare Advantage plan, move back to Original Medicare, change from one Medicare Advantage plan to another, or join, switch, or drop a Part D prescription drug plan. Any change made during this window takes effect on January 1, 2027.

A second, more limited window follows immediately afterward for people already enrolled in a Medicare Advantage plan. The Medicare Advantage Open Enrollment Period runs from January 1 through March 31, 2027, and allows a single additional plan change, either to a different Medicare Advantage plan or back to Original Medicare with a standalone Part D plan. This window is not available to people currently on Original Medicare, and it does not allow adding drug coverage to Original Medicare for the first time.

Medicare 2027 Enrollment Calendar

ACA Marketplace Open Enrollment 2027: Confirmed Dates

The ACA Open Enrollment calendar for 2027 coverage went through real uncertainty this year before CMS settled it. A federal regulation finalized in 2025 would have shortened the HealthCare.gov enrollment window, ending it on December 15 instead of the traditional mid-January date. A federal judge vacated that provision in June 2026, and in an August 2026 statement responding to ongoing litigation, CMS Deputy Administrator Peter Nelson confirmed in writing that open enrollment on the federally facilitated marketplace will run from November 1, 2026 through January 15, 2027, regardless of how the underlying appeal is eventually resolved.

That confirmed federal window applies to the 38 or so states that use HealthCare.gov directly. Several state-run marketplaces set their own, sometimes longer, deadlines, and shoppers in those states should use their state’s specific end date rather than the federal one.

ACA Open Enrollment 2027 Dates by State

Important note: enrolling after December 15, 2026 but before your state’s final deadline still gets you covered, but your plan will typically start February 1, 2027 instead of January 1, so anyone who needs coverage at the start of the year should not wait past the mid-December cutoff even though the overall window stays open longer in most states.

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Why This Year’s ACA Enrollment Season Is Different

Beyond the date confirmation itself, this year’s Open Enrollment carries more financial weight than usual because of what happened to ACA subsidies over the past year. The enhanced premium tax credits that had lowered marketplace premiums for more than 20 million enrollees since 2021 expired on December 31, 2025, after Congress failed to reach an agreement to extend them. The House passed a three-year extension bill in January 2026 with support from a group of Republicans who broke with their own leadership, but the Senate has not taken up or passed any matching legislation as of this writing, meaning the enhanced subsidies remain expired heading into the 2027 enrollment season.

With the enhanced credits gone, the original, pre-pandemic premium tax credit structure applies instead. That reverts eligibility back to households earning between 100 and 400 percent of the federal poverty level, and it increases the share of income that subsidized enrollees are expected to contribute toward their premium. According to analysis from health policy researchers, this shift already pushed average out-of-pocket premiums for subsidized enrollees sharply higher for 2026 coverage, and unless Congress acts before the 2027 plan year, that same higher-cost structure will carry into the coverage year that this Open Enrollment season determines.

Medicare Drug Plan Costs Are Also Shifting for 2027

Medicare’s enrollment dates may be unchanged, but the cost picture beneficiaries will see during this fall’s shopping window is not. CMS confirmed in July 2026 that it will end the Part D Premium Stabilization Demonstration after 2026, a temporary program that had been reducing standalone Part D drug plan premiums since 2025. The national base beneficiary premium for 2027 was set at $41.33, up from $38.99 in 2026, and CMS has said most beneficiaries should expect an increase of less than $10 a month, though plan-specific figures were not final at the time this article was first published.

Because both the Medicare AEP and the ACA Open Enrollment window ask shoppers to compare plan costs that are shifting for very different underlying reasons, financial counselors are urging people on both types of coverage to actually compare plans this year rather than allowing an existing plan to auto-renew, since a plan that was the cheapest option last year may not remain so once new pricing and subsidy rules are applied.

How to Apply for Coverage During Open Enrollment

The steps for enrolling differ slightly depending on whether you are shopping for Medicare or ACA Marketplace coverage, but both processes are designed to be completed entirely online, by phone, or with in-person help.

For Medicare coverage:

1. Review your current plan’s Annual Notice of Change, mailed by your plan before the AEP begins, to see how your premium and benefits are changing for 2027.
2. Compare available Medicare Advantage and Part D plans in your area using the Medicare Plan Finder tool on Medicare.gov.
3. Enroll in your chosen plan online, by calling 1-800-MEDICARE, or through a licensed insurance agent, between October 15 and December 7, 2026.
4. Confirm your new coverage takes effect January 1, 2027 through your MyMedicare.gov account.

For ACA Marketplace coverage:

1. Create or log into your account at HealthCare.gov or your state’s marketplace website.
2. Update your household income and family size, since this determines your eligibility for premium tax credits under the current, non-enhanced formula.
3. Compare available plans by premium, deductible, and covered providers, since your previous plan’s ranking may have changed under the new subsidy rules.
4. Select and enroll in a plan by December 15, 2026 to ensure coverage begins January 1, 2027, or continue enrolling through your state’s final deadline for coverage starting February 1, 2027.

Processing Time for Enrollment Applications

Both Medicare and ACA Marketplace enrollment are generally processed quickly once an application is submitted within the enrollment window. Medicare plan elections made during the AEP are typically confirmed within a few weeks, with the new plan’s membership card and materials arriving before the January 1 effective date. ACA Marketplace applications are usually processed within the same enrollment session online, though enrollees may need to submit additional income or identity verification documents if the system cannot immediately confirm eligibility, which can add several weeks to final approval if documentation is delayed.

Payment Schedule for 2027 Premiums

Medicare Part D and Medicare Advantage premiums are billed monthly, and beneficiaries can choose to have them deducted directly from Social Security payments, paid by direct debit, or billed by the plan itself. ACA Marketplace premiums are also billed monthly by the chosen insurer, with the first payment typically due before coverage becomes active on either January 1 or February 1, 2027, depending on enrollment timing. Enrollees receiving a premium tax credit will see that credit applied in advance each month, reducing the amount actually billed, based on the income estimate provided during enrollment; any difference between estimated and actual income is reconciled the following year when filing federal taxes.

Medicare & ACA Open Enrollment 2027 Deadline Calculator

Official Resources and Where to Enroll

Always confirm your state’s exact enrollment window and deadline directly through your marketplace’s official website, since some state-run exchanges may still adjust their calendars before the season begins.

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What to Watch Before and During This Enrollment Season

Two developments could still change the financial picture for millions of people even after enrollment opens. First, Congress could, in theory, act at any point to restore some version of the enhanced ACA premium tax credits, and health policy analysts have noted there is no hard legal deadline preventing a retroactive fix, meaning marketplace shoppers should watch for legislative movement throughout the enrollment period rather than assuming the current subsidy structure is permanently locked in for 2027. Second, CMS’s full Medicare Advantage and Part D landscape release, expected in mid to late September, will convert today’s national average figures into the specific plan premiums that actually matter for individual shopping decisions.

In the meantime, both Medicare beneficiaries and ACA Marketplace shoppers are best served by treating this year’s Open Enrollment as an active comparison exercise rather than a formality. With a major federal subsidy ending on the Medicare side and another major subsidy already gone on the ACA side, the plan that was cheapest for 2026 is not guaranteed to remain the best value for 2027.

Special Enrollment Periods: What Happens If You Miss the Window

Both Medicare and the ACA Marketplace offer limited exceptions for people who miss their standard enrollment window because of a genuine change in circumstances. On the Medicare side, a Special Enrollment Period can apply if you are losing employer coverage, moving out of your plan’s service area, or your plan is leaving the Medicare program entirely, among other qualifying events, and the specific rules and available time frame depend on the exact circumstance. On the ACA Marketplace side, qualifying life events such as losing job-based coverage, getting married, having or adopting a child, or losing eligibility for Medicaid typically open a 60-day Special Enrollment Period, allowing you to enroll in or change a Marketplace plan outside the standard November through January window.

Beneficiaries who experience one of these events should not assume they have to wait until next year’s Open Enrollment. Documenting the qualifying event and applying promptly, generally within 60 days of the event itself, is essential, since most Special Enrollment Periods do not allow retroactive enrollment once the window closes.

Common Mistakes to Avoid This Enrollment Season

With so many moving pieces this year, from expired ACA subsidies to an ending Medicare Part D subsidy, a few avoidable mistakes are showing up repeatedly in early guidance from insurance counselors. Letting a current Medicare Advantage or Part D plan auto-renew without comparing it against 2027 options is one of the most common, since a plan’s premium, formulary, and network can all shift year to year even when the plan name stays the same. On the ACA Marketplace side, failing to update household income before re-enrolling is another frequent error, since the loss of enhanced subsidies means even small income changes can meaningfully affect a household’s premium tax credit for 2027. Finally, waiting until the very last days of a state’s enrollment window is risky, since high site traffic and call center wait times tend to spike in the final week, and any documentation issues discovered late may not be resolved before the deadline passes.

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Conclusion

The Medicare and ACA Open Enrollment 2027 Dates are now fully confirmed: Medicare’s Annual Enrollment Period runs October 15 through December 7, 2026, while ACA Marketplace enrollment on HealthCare.gov runs November 1, 2026 through January 15, 2027, with several state-run marketplaces extending their windows into late January. Behind these dates sits a genuinely different cost environment than last year, with enhanced ACA subsidies still expired after Congress failed to renew them and a separate Medicare Part D premium subsidy ending after 2026. Anyone with Medicare or Marketplace coverage should treat this enrollment season as a chance to actively compare plans, watch official sources for final premium figures, and enroll before the applicable mid-December deadline if January 1 coverage matters to them.

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