In short, acts of homophobic social exclusion - violence, job loss, discrimination, etc. - lead to individual-level shortcomings in education and earnings, which then translate into economy-level impacts such as higher healthcare and social program costs, and lower economic output.
Depending on which estimate one goes with on the homosexual population of India - a task made difficult by underreporting combined with Indian ideas of sexuality that don't necessarily line up neatly with the Western LGBT quartet - the economic cost of homophobia is between $1.9 billion and $30.8 billion annually, or .01% to 1.7% loss to the GDP. A GDP reduction of that amount would be considered a recession, according to the study's author, University of Massachusetts economist Lee Badgett.
The findings aren't conclusive and the study acknowledges that more research needs to be done. Areas of particular attention going forward will be investing in data on LGBT exclusion, a focus on poverty, research infrastructure, and replicating the study in other countries.
You can see a video of the presentation, which clocks in at a hefty 2 hours, AFTER THE JUMP...