U.S. Defense Secretary Ash Carter backed admitting openly transgender people into the military last month. A new study suggests the costs would be minimal. Getty Images

Caring and treatment for transgender people serving in the U.S. military would cost taxpayers what amounts to "little more than a rounding error," or about $5.6 million a year. The prospective healthcare costs have been the subject of scrutiny since Defense Secretary Ash Carter supported admitting openly transgender people into the military for the first time last month.

Last week, during the first debate for Republican presidential candidates, former Arkansas Gov. Mike Huckabee said, "I'm not sure how paying for transgender surgery for soldiers, sailors, airmen, Marines makes our country safer." But apparently the costs would be negligible compared to the $47.8 billion healthcare tab the military faces every year, and especially compared to the overall military budget, pegged at $585 billion for 2015.

Estimated Transgender Individuals per 100,000 People | FindTheBest

Of the 12,800 transgender people estimated to be in the military, about 188 are predicted to be in treatment annually, said Aaron Belkin, an academic at San Francisco State University. Treatment costs about $30,000 for hormone therapy, surgery or both, and usually takes about six-and-a-half years to complete. The overall cost to the military is small, partly because it will save on mental-health costs.

Belkin told Reuters that the military has a transgender population that is estimated to be two times as high as that of 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.

The move to admit openly transgender people into the military follows a 2011 decision to repeal "don't ask, don't tell," the Clinton-era law that prohibited gay service members from disclosing their sexual preferences. It is also accompanied by the high-profile case of Chelsea Manning, a former intelligence analyst currently serving a 35-year prison term for disclosing state secrets on WikiLeaks. Manning disclosed her preference to live as a woman instead of a man following the leaks.

In civilian life, private-sector corporations are increasingly likely to cover the costs of transgender therapy. About one-third of Fortune 500 companies offer healthcare plans that are trans-inclusive. The rise of transgender healthcare inclusion was spearheaded by San Francisco's decision to cover transgender people, which proved not to be incredibly costly.