Several Civil War authors often mention how Lee "Bled his army White" by his constant attacks or call Hood a "butcher" as opposed to Joe Johnston (See Attack and Die for example) who it is asserted cleverly fought a defensive battle vs. Sherman. But the facts are that offense and defense were almost equally costly. Here are the numbers:
Johnston Lost Killed and Wounded (May to July 18th 1864) - 10,000
Hood Lost Killed and Wounded (July 18th to September 1, 1864) - 12,500
Meanwhile the Army of the Tennessee lost May to September 1, 1864 - 10,000 POW.
The POW's are not broken out by Month in Sherman's Memoirs -but its obvious most were lost on the defense under Johnston vs. attacking under Hood. If we allocated them 6,000 to Johnston and 4,000 to Hood we get the following causalities for the Atlanta Campaign:
Johnston (the clever Fabian) - 16,000 KIA, WIA, POW
Hood (the "Butcher") - 16,500 KIA, WIA, POW
Meanwhile look at Sherman's Loss (WIA/KIA/POW):
May to July 18th 1864 (vs.Johnston) - 18,500*
July 18th to Sept 1, 1864 (vs. Hood) - 11,500
Total - 30.000
* Sherman lost 9,000 men from July 4th to July 31, 1864 in the Battle Of Atlanta. I have assumed 1,500 were against Johnston from July 4th to July 18th; since Johnston lost 552 men Killed and Wounded during the same period. This number is reasonable based on the fact that Sherman lost 6,300 in three major battles against Hood in July. That leaves 2,700 casualties - or about 100 men per day. July 4rd to July 18th is 15 days.