ACA marketplace enrollment dropped by nearly three million people nationally between February 2025 and February 2026 — driven largely by subsidy expiration and rising premiums. Others stayed on their marketplace plan past 65, still paying premiums on coverage they should have transitioned away from. Advanced Premium Tax Credits — the subsidies that lower your monthly marketplace premium — are not available once you become eligible for Medicare. Having ACA marketplace coverage does not extend or replace this window. For both groups, the Medicare enrollment window is either approaching or already in motion.