World leaders are failing 1.4 billion girls and women on promises of a fairer future, according to a global index launched at the world's biggest gender equality conference.

The research shows the world is way off track to meet a 2030 deadline for achieving gender equality, with not one country having reached the "last mile."

Japan ranked 21st on the index with a score of 80.6, behind countries such as Australia (85.2) and Italy (81.8), but ahead of the United States, ranked 28th with a score of 77.6, and South Korea at 41st place with a score of 72.6.