Medicare's standard for when a hospital stay is billed as inpatient. The benchmark, the exceptions, Medicare Advantage rules, who reviews short stays since 2025, and the inpatient-only phase-out.
The two-midnight rule is Medicare's standard for when a hospital stay should be billed as an inpatient admission under Part A rather than as outpatient care. In short: inpatient admission is generally appropriate when the admitting physician reasonably expects the patient to need hospital care spanning at least two midnights, and the medical record supports that expectation. This reference covers what the rule says, the exceptions, who it applies to, who reviews it, what has changed since 2024, and why it matters to coding.
What the two-midnight rule says
The rule is codified at 42 CFR 412.3 and took effect for admissions on or after October 1, 2013. It has four working parts.
| Part | Regulation | What it says |
|---|---|---|
| Inpatient order | 412.3(a) to (c) | A patient is an inpatient only after a formal inpatient order from a qualified practitioner with admitting privileges, written at or before admission |
| Two-midnight benchmark | 412.3(d)(1) | Admission is generally appropriate when the physician expects care to cross two midnights, based on complex medical factors documented in the record |
| Inpatient-only procedures | 412.3(d)(2) | Procedures on Medicare's inpatient-only (IPO) list are appropriate for inpatient admission regardless of expected length of stay |
| Case-by-case exception | 412.3(d)(3) | Admission expected to last less than two midnights may still be appropriate, based on the physician's judgment and the record |
Three points trip people up.
It's the expectation that counts, not the actual stay. If a patient expected to stay two midnights is discharged early because they improved quickly, transferred or died, the admission can still be appropriate. The question is whether the expectation was reasonable when the order was written.
Time before the order counts toward the benchmark. Under CMS guidance from the FY2014 inpatient rule, the two-midnight expectation includes hospital care already received in the emergency department, observation or outpatient surgery before the inpatient order. That earlier time does not count toward the three-day inpatient stay Medicare requires for skilled nursing facility coverage, which counts inpatient days only.
The documentation has to show why. The complex medical factors behind the expectation (history, comorbidities, severity of signs and symptoms, current medical needs and risk of an adverse event) must be in the record when the decision is made. Notes written later can explain the decision but can't create it.
The presumption and how short stays are reviewed
The rule has a review counterpart, often called the two-midnight presumption. Inpatient stays that cross two midnights after the inpatient order are generally presumed appropriate and are not the focus of Medicare's patient status reviews. Short stays, those spanning fewer than two midnights after the order, are where reviewers look.
Who does that review changed recently. According to CMS's hospital patient status review FAQ, the Beneficiary and Family Centered Care Quality Improvement Organization (BFCC-QIO) concluded its short-stay reviews in August 2025, and the Medicare Administrative Contractors (MACs) took over on September 1, 2025, under the Targeted Probe and Educate approach. Reviewers judge the physician's expectation at the time of the order, and the MACs won't use the 48-hour observation allowance as a test of whether inpatient admission was appropriate.
The case-by-case exception
Since the CY2016 outpatient rule, an admission expected to last less than two midnights can still be paid under Part A when the physician's judgment and the record support inpatient care. CMS has said that a stay that doesn't span even one overnight is unlikely to warrant inpatient admission and is a review priority.
This exception is where documentation quality decides the outcome. "Admit to inpatient for chest pain" will not hold up for a one-midnight stay. A note that records an elevated troponin, a history of prior stents, renal insufficiency affecting contrast use and a plan for urgent catheterization makes the case.
Who the rule applies to
| Payer | Does the rule apply? |
|---|---|
| Traditional Medicare (Part A) | Yes, in full, including the benchmark, exceptions and review approach |
| Medicare Advantage | Yes for the admission criteria; no for the review presumption |
| Medicaid and commercial plans | Not by federal rule; depends on state rules and contract terms |
| Critical access hospitals | The order and benchmark apply, with the CAH's separate conditions |
The Medicare Advantage row comes from the CY2024 MA final rule (CMS-4201-F), effective January 1, 2024. CMS's February 2024 FAQ says MA plans must follow the inpatient admission criteria in 42 CFR 412.3, including the two-midnight benchmark, but do not have to follow the presumption that applies to traditional Medicare review contractors. It also says an algorithm or AI tool cannot be the sole basis for denying an inpatient admission. MA plans can still use prior authorization and concurrent review to check the record.
In practice this means an MA plan can still deny an inpatient stay, but the denial has to engage with the same expectation-based standard traditional Medicare uses.
Inpatient-only procedures and the phase-out
Procedures on the IPO list have been payable as inpatient regardless of expected length of stay. That list is shrinking fast.
- CY2026 final rule: CMS began a three-year phase-out of the IPO list, starting January 1, 2026.
- CY2027 proposed rule: released July 2, 2026, it proposes removing 638 more procedures effective January 1, 2027, nearly half of what remains. The final rule is expected in early November 2026.
Removal doesn't require outpatient care. It means the procedure no longer gets automatic inpatient status, so the admission must meet the two-midnight benchmark or the case-by-case exception like any other. Under 412.3(d)(2), procedures removed from the list on or after January 1, 2021 are exempt from certain medical review activities until CMS decides they're more commonly performed as outpatient. That protects against Medicare patient status audits, but it may not protect against MA plans, which apply the admission criteria directly.
What the rule means for coding
Patient status isn't a coding decision, but it decides what gets coded and how.
| Status | Claim | Diagnosis rules | Payment basis |
|---|---|---|---|
| Inpatient | UB-04 type of bill 11x | Inpatient guidelines; uncertain diagnoses at discharge coded as if confirmed | MS-DRG |
| Outpatient, including observation | UB-04 type of bill 13x | Outpatient guidelines; uncertain diagnoses not coded | APC under OPPS |
Four practical consequences for coding and CDI teams:
- Check the order before coding. A chart coded to an MS-DRG without a valid, timely inpatient order is a billing error regardless of coding accuracy.
- Code to the status on the claim. The same chest pain patient produces different principal diagnoses, code sets and payment depending on status. Our guide to observation, inpatient and ED status walks through one patient coded three ways, including condition code 44 when status changes before discharge.
- Watch short stays. One-midnight inpatient claims are the highest review risk. CDI can flag whether the record states the expectation and the complex factors behind it before the claim drops.
- Track IPO removals each January. A procedure removed from the list changes from automatic inpatient to expectation-based. Update charge masters, scheduling rules and any coding edits that assume inpatient status.
- Remember POA timing. The inpatient order also sets the present on admission indicator for every diagnosis on the claim.
Most short-stay patients reach the hospital through the emergency department, so status decisions start there. See our ED coding automation guide for how ED documentation feeds the admission decision. For inpatient cases where the principal diagnosis is disputed after admission, see our guide to sepsis coding and payer clinical validation.
Timeline and update cycle
| Date | Change |
|---|---|
| Oct 1, 2013 | Two-midnight rule takes effect (FY2014 inpatient rule) |
| Oct 1, 2015 | BFCC-QIOs take over short-stay reviews from Recovery Auditors |
| Jan 1, 2016 | Case-by-case exception for stays under two midnights (CY2016 outpatient rule) |
| Jan 1, 2024 | Medicare Advantage plans required to follow 412.3 admission criteria (CMS-4201-F) |
| Sep 1, 2025 | MACs take over short-stay patient status reviews from the BFCC-QIO |
| Jan 1, 2026 | Three-year IPO list phase-out begins (CY2026 outpatient final rule) |
| Jan 1, 2027 | Proposed removal of 638 more IPO procedures (CY2027 outpatient proposed rule) |
Changes to the rule arrive through two annual cycles: the inpatient rule (proposed in spring, final in August, effective October 1) and the outpatient rule (proposed in summer, final in November, effective January 1). The IPO list moves with the outpatient rule.
Frequently asked questions
What is the two-midnight rule in simple terms?
Medicare generally pays a hospital stay as an inpatient admission when the admitting physician reasonably expects the patient to need hospital care across at least two midnights, and the record documents why. Shorter expected stays are usually billed as outpatient care, including observation, unless an exception applies.
Does time in the ED or observation count toward two midnights?
Yes for the two-midnight expectation: hospital care received before the inpatient order counts toward the benchmark. No for skilled nursing facility coverage, where Medicare counts only days after the inpatient order toward the three-day stay requirement.
Do Medicare Advantage plans have to follow the two-midnight rule?
Since January 1, 2024, MA plans must follow the inpatient admission criteria in 42 CFR 412.3, including the two-midnight benchmark. They don't have to apply the review presumption used by traditional Medicare contractors, and they can't deny an admission based on an algorithm alone.
Can a one-midnight inpatient stay be appropriate?
Yes, under the case-by-case exception, when the physician's judgment and the documented complex medical factors support inpatient care. A stay that doesn't span even one overnight is unlikely to qualify and is a review priority.
What happens if the hospital changes the patient from inpatient to outpatient?
If utilization review finds the inpatient order wasn't supported before discharge, the hospital can change the status to outpatient using condition code 44, provided the physician agrees and the change is made while the patient is still in the hospital. The claim is then billed as outpatient.
Sources
- 42 CFR 412.3, Admissions (eCFR)
- CMS Hospital Patient Status Review FAQ
- CMS Fact Sheet: Two-Midnight Rule (CY2016 update)
- CMS FAQ on coverage criteria in CMS-4201-F (February 2024)
- ACDIS: CY2026 OPPS final rule begins IPO phase-out
- Davis Wright Tremaine: CY2027 IPO proposal
This reference is general education on Medicare policy. It is not legal advice or a determination about any specific admission. Patient status decisions belong to the admitting physician, and payer contracts may add requirements.
