Updated August 7, 2026. Quick answer: “Medicare covers 100 days of rehab” is the most expensive half-truth in post-hospital care. 🔴 Medicare pays in full for 20 days. Days 21 through 100 carry a daily coinsurance amount — and the benefit can end long before day 100 for a reason that has nothing to do with the calendar.
The 20 and the 80
The regulation sets it out plainly:
Up to 100 days are available in each benefit period after discharge from a hospital or CAH. For the first 20 days, Medicare pays for all covered services. For the 21st through 100th day, Medicare pays for all covered services except for a daily coinsurance amount that is the beneficiary’s responsibility.
🔴 Days 21 to 100 are 80 days of daily coinsurance. That is the number families should be planning around, and it is the one the phrase “100 days” conceals. This page does not print the coinsurance figure because it is set annually — ask the facility what this year’s daily amount is, in dollars, before day 21.
⚠️ Many people have secondary coverage that picks up that coinsurance. Whether yours does is a question to ask now, not on day 22.
The 100 days renew — the lifetime reserve does not
The benefit is per benefit period, not per lifetime:
The beneficiary’s full entitlement to the 90 inpatient hospital… regular benefit days, and the 100 SNF benefit days, is renewed each time he or she begins a benefit period. However, once lifetime reserve days are used, they can never be renewed.
Two different rules sitting next to each other, and confusing them costs money in both directions — people assume the SNF days are gone forever when they are not, and assume the lifetime reserve days will come back when they will not.
🔴 Why the benefit usually ends before day 100
The days are a maximum, not an entitlement. Coverage continues while the care meets Medicare’s requirements — and in practice a stay very often ends well short of 100 days because the facility determines the covered care is no longer needed.
When that happens you are handed a notice, and it is on a brutally short clock. A Notice of Medicare Non-Coverage requires the fast-review request by noon of the calendar day after you receive it, and missing that deadline does not end the appeal — it ends the financial protection. The whole mechanic is on the NOMNC page, and it is the single most time-critical thing in this entire subject.
And none of it happens without the three days
All of the above assumes the stay qualified in the first place, which turns on a word most patients never hear: observation is not inpatient, and only inpatient days count toward the required three.
Sources
Quoted from 42 CFR § 409.61 (duration of covered inpatient and posthospital SNF services), via eCFR, retrieved 7 August 2026: ecfr.gov. No dollar figures appear on this page — the coinsurance amount is set annually and the only reliable version is the current one.