This article introduces the Nonprofit Virtual Accountability Index (NPVAI) as a tool for nonprofits to strategically plan their online accountability, as well as for researchers to empirically analyze nonprofit Web sites. The index is developed first from the theoretical literature on nonprofit accountability, on government virtual accountability, and on best practice in website design. An exploratory factor analysis is then carried out on the index adapted from these sources. The nonprofit virtual accountability components identified were accessibility, engagement, performance, governance, and mission. The index is applied to nonprofits in Illinois to test its validity. The findings confirm the validity of the index as a tool to measure nonprofit virtual accountability.