Acts on page turns
The tool takes the non-story pages before and after the story off your interior count, splits the story pages 25/50/25 into three acts and reports each act's range as book page numbers, rounded so acts start on whole pages and always add up to the total. It then tells you whether each act ends on a right-hand page (a page turn, good for a cliffhanger) or a left-hand page (mid-spread, no turn). A page before the story moves every act break by one, so moving a credits or recap page to the front can land an act break on a turn.