Medicare Part A start dates and the first-day birthday rule
Identify the HSA cutoff month around age 65, including the earlier start for a birthday on the first of a month.
Premium-free Part A generally begins the month a person turns 65 when enrollment is timely. A birthday on the first day generally moves coverage to the prior month.
Use the effective date, not application date
Eligibility to enroll, the application, and coverage start are different. Obtain the official Medicare effective date and use the first day of that month as the HSA contribution boundary.
Recalculate final-year room
Apply the monthly limit for months before Medicare. Catch-up amounts are also subject to monthly eligibility when the person is not eligible all year.
Example and common mistake
A person turns 65 on June 1 and Part A starts May 1. April may be the last eligible month. Assuming everyone may contribute through the month before the numerical birthday is the mistake.
Use the entitlement date, not the card date
Review the Medicare entitlement notice for the Part A effective month. The rule can differ for enrollment before 65, during the initial enrollment period, or after delayed enrollment tied to work coverage. The date an identification card arrives and the date premiums are paid do not establish HSA contribution eligibility.
Apply the first-day-of-month rule to the effective date, including special birthday timing when coverage starts before the birthday month. Keep the notice with the annual HSA workpaper. If the date is retroactive, recalculate eligible months and address excess contributions rather than merely stopping future deposits.
Questions to resolve
- Which entitlement month appears on the Medicare record?
- Does birthday or enrollment timing move coverage before the expected month?
- Has the monthly HSA limit been recalculated for any retroactive period?
Federal authority record
- CMS / Medicare.gov: When does Medicare coverage start?
Part A effective dates, first-day birthdays, and retroactive enrollment - CMS / Medicare.gov: Medicare & You 2026
Medicare start dates, retroactive Part A, and HSA contribution stop guidance - IRS: Publication 969 — HSAs and other tax-favored health plans
Monthly eligibility, last-month rule, spouses, Medicare, and excess contributions