Figuring out how many troops the U.S. has in a war zone such as Afghanistan is never easy.

The numbers fluctuate as units move in and out, and military leaders don't like to telegraph troop strength, particularly the more secretive special operations forces, to the enemy.

But the Pentagon also doesn't count scores of troops that are often in the country for months at a time. In many cases it's because they are considered temporary for some administrative reason or other.

As a result, the fuzzy math doesn't always add up.

On Wednesday, President Barack Obama scrapped plans to cut American forces in Afghanistan by half before he leaves office in January. He said he will leave 8,400 troops to address Afghanistan's "precarious" security situation.

A look at the Afghanistan numbers:

NOW:

— There are about 9,800 U.S. troops in Afghanistan.

— About 6,900 are part of NATO's train, advise and assist mission aimed at working with Afghan army and police

— The rest are conducting counterterrorism missions against al-Qaida, Taliban and Islamic State militants, and doing other related jobs.

— other nations are contributing about 5,500 troops to the NATO advisory mission.

FUTURE:

— Obama says the U.S. will reduce its troop presence to 8,400 by year's end.

— U.S. Army Gen. Curtis Scaparrotti said about 6,700 will remain part of the NATO mission. That would leave 1,700 for other duties.

— A senior U.S. administration official said the U.S. will continue to have more than 2,000 forces committed to the counterterrorism mission — which would add up to 8,700 total, using Scaparrotti's figures. The official was not authorized to discuss the numbers publicly and spoke on condition of anonymity.

— But some U.S. troops may perform double duty, at times doing the training mission and other times doing counterterrorism operations.

— Also, some U.S. troops may be among those that are not formally counted.

— Officials say they expect the other NATO nations to contribute roughly the same as they have been.