Free tool

ALOS calculator

Average length of stay (ALOS) is how many days, on average, a discharged inpatient occupied a bed. Enter your numbers below — the calculator updates as you type, and already shows a worked example.

Updated 14 September 2026

In short

ALOS = total inpatient days of discharged patients ÷ number of discharges in the period. 620 inpatient days across 124 discharges works out to an ALOS of 5.0 days.

Formula: Inpatient days ÷ Discharges
Needs: Total inpatient days, number of discharges, same period
Related: Bed occupancy rate, census

Calculator

Total inpatient days (discharged patients)Sum of (discharge date − admission date) across every patient discharged in the period.

Number of discharges in the periodCount every discharge, including deaths and transfers out, for the same period.

Average length of stay5.0 days

620 inpatient days across 124 discharges.

The formula

ALOS (days) = Total inpatient days of discharged patients ÷ Number of discharges

A single patient's length of stay is their discharge date minus their admission date — a patient admitted and discharged on the same day counts as one day of stay. "Total inpatient days" is the sum of that figure across every patient discharged in the period you're measuring (not every patient who was in a bed at some point during it), and the denominator is the count of those same discharges. Some hospitals divide by admissions instead of discharges — either is defensible, but be consistent about which one you use so figures stay comparable over time.

Worked example

If your ward discharged 124 patients in a month, and those patients' stays add up to 620 inpatient days in total, ALOS is 620 ÷ 124 = 5.0 days — the same numbers the calculator above starts with.

Getting the inputs right

Keep the numerator and denominator over the same window: total inpatient days should only include the stays of patients you're also counting in the discharge figure, for the same period. A patient who is still admitted at month-end doesn't belong in either number yet — their stay contributes to next period's ALOS once they're discharged, not this one's. Same-day admissions and discharges are usually counted as a one-day stay rather than zero, so they still add to the numerator; if you exclude them instead (some day-case or short-stay reporting does), say so alongside the figure, since it changes the average meaningfully for a busy short-stay ward.

How to read the result

ALOS is a summary of a mix of very different stays — a handful of long admissions can pull the average up even when most patients leave quickly, so a single ALOS figure hides that spread. It's most informative watched over time for a comparable group of patients (the same ward or specialty), and read alongside bed occupancy rate: rising occupancy with a falling ALOS usually means more patients are moving through the same beds, while rising occupancy with a rising ALOS points to beds staying full because patients are staying longer. This page doesn't name a target ALOS — what's typical varies enormously by specialty and case mix.

In Trisvio

Census, ALOS and bed occupancy — computed automatically

Trisvio's MIS reports compute ALOS directly from your admission and discharge records alongside daily census and bed occupancy. See how it works on the hospital analytics feature page.

See how it works Request a demo

Official references

Average length of stay, all hospitals — indicator definition ↗WHO Regional Office for Europe, European Health Information Gateway

Rules change. Confirm current requirements with the issuing authority.

More on hospital capacity and inpatient flow.