LONDON (Thomson Reuters Foundation) - Transition care for transgender members of the U.S. military would cost around $5.6 million a year, “little more than a rounding error” as a share of total expenditure, according to new research published amid criticism of proposed funding.

The sum amounts to just 22 cents per service member per month, said Aaron Belkin, an academic at San Francisco State University, adding that the military’s annual healthcare budget is currently $47.8 billion.

Last month, defense chief Ash Carter backed the admission to the U.S. military of openly transgender people for the first time, setting up a working group to study the issue “with the presumption that transgender persons can serve openly without adverse impact”.

Some criticized Carter’s decision. “I’m not sure how paying for transgender surgery for soldiers, sailors, airmen, Marines makes our country safer,” Mike Huckabee, a presidential candidate, said in the first Republican debate last Thursday.

By estimating how many closeted transgender people currently serve in the military, and looking at what has happened in Australia, which already funds transition-related care, Belkin predicts around 188 service members would get care annually.

Treatment, which can involve surgery, hormone therapy or both, costs just under $30,000 and takes six and a half years on average, the study in the New England Journal of Medicine said.

It takes into account the fact that transgender people are twice as common in the military as in the general population.

“This is possibly because many transgender women - those born male but identifying as female - seek to prove to themselves that they are not transgender by joining the military and trying to fit into its hypermasculine culture,” Belkin said.

Chelsea Manning, a former intelligence analyst serving a 35-year sentence for leaking classified information to pro-transparency site WikiLeaks, announced in August 2013 that she would live as a woman rather than as a man named Bradley.

The overall costs could be lower because treatment has been proved to help serious mental health conditions that may cost more in the long run, Belkin said. “There are costs, in other words, of not providing transition-related care.”

“Don’t Ask, Don’t Tell”, a 1993 law prohibiting openly gay people from military service, was formally repealed in 2011.