Over at Foreign Policy, Michah Zenko, a fellow at the Council on Foreign Relations, has taken a critical look at the estimates of Daesh fighters the U.S. has killed provided by various Department of Defense sources since 2015. Despite several about-faces on a policy of releasing such figures, the lure to do so is powerful because of the impact they have on public opinion.
Zenko notes the inconsistent logic in the the numbers released, the lack of explanation of the methodology at how they were derived, and how denials about their validity undermine the public policy value of providing them in the first place. There is also the problem of acknowledging noncombatant deaths but asserting that only 55 civilians have been killed in over 15,000 confirmed airstrikes.
Here is the list Zenko compiled of Defense Department cumulative estimates of Daesh fighters killed in Iraq and Syria by U.S. airstrikes:
January 2015: 6,000
March 3, 2015: 8,500
June 1, 2015: ~13,000
July 29, 2015: 15,000
October 12, 2015: 20,000
November 30, 2015: 23,000
January 6, 2016: 25,500
April 12, 2016: 25-26,000
August 10, 2016: 45,000
Chris cited an article two weeks ago in the New York Times, that provided an estimate by a Defense Department source that there are currently 19-25,000 Daesh fighters in Iraq and Syria.