Under Original Medicare Part A, a covered skilled nursing facility (SNF) stay inside a benefit period commonly uses day-band cost sharing: many people owe $0 coinsurance for days 1–20 of covered skilled care (after benefit-period deductible rules), then a daily coinsurance for days 21–100 that CMS publishes each calendar year. After day 100 in that benefit period, you generally pay in full for continued SNF care unless other coverage applies. Benefit-period and 100-day clock: Skilled nursing benefit period basics. Part A frame: Medicare Part A benefit period basics. Why observation status can block the path: Observation status vs inpatient basics.
This page is the patient-pay / copay math—not a full benefit-period tour and not custodial long-term nursing-home coverage.
Day bands at a glance
| SNF days in the benefit period (illustrative Original Medicare) | Typical patient coinsurance | Watch-out |
|---|---|---|
| Days 1–20 | Often $0/day for covered skilled days after deductible rules | Part A deductible may already have been owed for the hospital stay in the same period |
| Days 21–100 | Daily coinsurance (CMS sets the dollar amount yearly) | This is the band Medigap letters often target |
| After day 100 | Patient-pay unless other coverage applies | New benefit period needs the 60-day break rules |
Always use Medicare.gov or your Medicare Summary Notice for this year’s daily figure—blog placeholders go stale. Skilled care must meet Medicare’s skilled criteria; room-and-board custodial care alone is a different bill.
How Medigap and Advantage change the copay
Standardized Medigap plans (letters) often pay the Part A SNF coinsurance for days 21–100 per their outlines of coverage. Shop letters during open enrollment or guaranteed-issue windows when you qualify. Premiums from UnitedHealthcare, Humana, Mutual of Omaha, regional Blues, and others are separate from the daily SNF coinsurance itself.
Medicare Advantage plans use plan SNF copays, prior authorization, and network SNFs—not the Original Medicare day-band table blindly. Read the Evidence of Coverage for day-1 vs day-21 language and any daily maximums. Bill habits: Medical bills and insurance.
Worked example: 35 SNF days with and without Medigap
Morgan has Original Medicare after a qualifying inpatient hospital stay (not observation). Morgan uses 35 covered SNF days in one benefit period. Illustrative CMS figure for Morgan’s year: $209.50/day coinsurance for days 21–100 (placeholder—use the official amount).
| Scenario | Days 1–20 | Days 21–35 (15 days) | Illustrative patient total |
|---|---|---|---|
| No Medigap | $0/day | 15 × $209.50 ≈ $3,142.50 | ≈ $3,143 coinsurance |
| Medigap letter that covers SNF coinsurance | $0/day | Plan pays the daily coinsurance per outline | ≈ $0 SNF coinsurance (premiums still apply) |
If Morgan instead has a Medicare Advantage plan with a $200/day SNF copay starting day 1 (illustrative), 35 days could mean a very different total—trust the EOC, not the Original Medicare table.
Practical habits
- Confirm inpatient vs observation before you assume SNF eligibility or day-band math.
- Look up this year’s official SNF coinsurance on Medicare.gov the week a stay may cross day 20.
- Ask the SNF billing office which benefit-period day you are on (1–20 vs 21–100).
- Read your Medigap outline specifically for SNF coinsurance—or confirm you have none.
- If on Advantage, use that plan’s SNF copay schedule and prior-auth rules.
- Save MSNs until day counts and coinsurance match your calendar.
Checklist
- Confirm Original Medicare (A + B) vs Advantage before applying day-band copays.
- Verify a qualifying inpatient hospital stay when Original Medicare SNF rules apply.
- Budget for daily coinsurance if a stay may cross day 20.
- Match Medigap letter charts to SNF coinsurance—or price the gap in cash.
- Note whether a later stay continues the same benefit period or starts a new one.
- Re-shop supplemental coverage only with current letter charts and SHIP help.
Lifetime reserve days are a hospital pool, separate from SNF copay bands: Medicare lifetime reserve days basics. Home health periods are not the SNF 100-day table: Home health episode of care basics.
Educational only. Not insurance, tax, legal, or medical advice. Not a plan recommendation. Part A SNF day bands, coinsurance amounts, qualifying-stay rules, Medigap letter benefits, and Advantage designs change; confirm with Medicare.gov, your state SHIP program, the SNF, and insurer outlines of coverage.