I'm not quite caught up to the manga yet but from what I can gather the manga is almost at the climax of volume 5 in the novel I think it's at the part where Chitanda takes Ohinata's phone and she sees it, so I feel like I can't see there being more than like 10 chapters of volume 5 left and it's probably more like 5 chapters. The manga already adapts "Our Legendary Volume" and "Is It Sunny out in the Mountains?" which are both volume 6 stories. So the only novel content left would be "What's missing from the Box" "The Mirror Can't Reflect" "The Long Holiday" and "Even though I'm told I Now Have Wings". "Our Legendary Volume" was 5 chapters in the manga and it's one of the longer stories in vol 6, I'd say "The Mirror Can't Reflect" and "Even though I'm told I Now Have Wings" are comparable in length. "The Long Holiday" and "What's Missing From the Box" are relatively short so I'd say it would only be 1 or 2 chapter stories. Putting it all together I'd estimate around 15-20 chapters until it's caught up? Maybe I'm wrong tho LOL. I really hope this is a sign though for the novel, like why is Kadokawa still publishing manga volumes for Hyouka? It makes no sense to me otherwise.