Board Thread:Episode Discussions/@comment-1018594-20170628094736/@comment-734582-20170701100916

Mr. Grave wrote: We were never given an estimate on how much the Sharingan has depleted his chakra reserves. Judging from how others use it, i'd say it was a massive chunk of his chakra. Sasuke could keep two active with little to no cost. His chakra levels were comparable pre-curse mark (I think Kakashi could use 6 and Sasuke 3 chidori or so). Others like Itachi could keep them active even during non-critical scenarios. So for a True Owner the chakra cost is quite low.