The WHO Global strategy on human resources for health: workforce 2030 encourages development partners and global health initiatives to leverage their support to health systems in countries to sustainably strengthen the health workforce. To assess the impact of these investments, a methodology was developed and pilot tested by WHO. The impact assessment tool (consisting of an MS Excel calculator with two subsets) supports users to: • assess and quantify the health impact of HRH investments made in the context of HIV, tuberculosis (TB) and malaria programmes through their modelled effect on health service coverage of these three diseases; and • provide aggregate indicative estimates of the range of health workers required to attain high coverage of selected health services.