The Weighted Activity Unit (WAU)

The Weighted Activity Unit (WAU) is a 'common currency' to describe an amount of clinical activity, with a weighting applied that takes account of casemix and complexity.

This video explains how we use WAUs in the Model Hospital.


A WAU is quantity of any types of clinical activity including inpatients, outpatients, diagnostic testing and others. We take the national average cost of each clinical activity, and divide it by 3,500 to say how many WAUs that clinical activity is ‘worth’. The national average cost of a procedure comes from reference costs. One WAU equates to £3,500 ‘worth’ of healthcare services.

Lord Carter introduced the WAU in his report into productivity in NHS hospitals. Very similar concepts are widely used internationally, such as Adjusted Admissions in the US and the National Weighted Activity Unit in Australia.

It is used as a denominator in productivity calculations (such as cost per WAU, FTE per WAU, or number of linen items per WAU). Cost per WAU can be broken down into different cost elements to highlight which areas a trust appears to be spending more than their peers.

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