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Understanding Length of Stay

The term “length of stay” (LOS) in health care refers to the period of time (in days) that spans from when a patient was admitted to the hospital to the time they are discharged.

Typically this is reported as an average. However, the average length of stay does not compare “apples to apples”, because it assumes all the patients are the same. In reality, every patient is unique and some are sicker than others or have co-existing illnesses that make their condition more complicated to treat.

At UTMB Health, we use a measure known as length of stay index to compare ourselves to other hospitals (see "Calculating Length of Stay" below for more).


Academic medical centers like UTMB Health provide higher levels of specialized patient care and provide advanced treatments and surgeries. Therefore, our patients are typically sicker than those at community hospitals.

Length of stay is an important consideration for several reasons:

  • The longer a patient is in the hospital, the longer they are exposed to germs and illnesses they may not have otherwise been exposed.
  • Patients do not want to be away from the comfort and convenience of home for longer than necessary.
  • The longer you are in the hospital, the more it costs.

It is important to keep in mind that hospitals should not discharge patients before their care is complete, because it could result in readmission.

Calculating Length of Stay

Observed Average Length of Stay

The observed average length of stay is average amount of time (in days) that patients stayed in the hospital during a given time period. It is calculated by adding the total time each patient was in the hospital and dividing that number by the total number of patients discharged.

Expected Average Length of Stay

The expected average length of stay represents the average amount of time (in days) during a predicted to stay in the hospital. UTMB Health’s expected average length of stay is calculated by a company called UHC. The expected mortality is risk-adjusted, meaning that other variables (such as age, race, other illnesses, and the severity of their illnesses) are considered because these can affect the length of stay. UHC provides a description of the variables they use in their risk model no their website.

Length of Stay (LOS) Index

The length of stay index compares the actual length of stay to the expected length of stay. The length of stay index is calculated by dividing the observed length of stay by the expected length of stay. A score of 1 means that patients were in the hospital for the amount of time that was predicted. A score of less than 1 means that more patients spent less time in the hospital than was predicted. A score of more than 1 means that patients spent more time in the hospital than was predicted. So, a lower the score is better.

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