@Village-Idiot said in Light novels and their manga adaptions:
The manga is usually just to promote the LN and very rarely actually finishes completely adapting the LN.
The usual rate is around two manga volumes per LN.
That's what happened recently with Ester de Valonia/エステルドバロニア (currently 2 light novel volumes, 4 webnovel volumes)
It had a 10-chapter manga adaptation, and despite the author's wishes it was cut short thereafter.
(Turned out pretty popular with the English readers, turning into some drama when they saw a note on the last page of chapter 10 which said volume 2 comes out on January 27th and were sure it meant it was going to continue, all the while others tried in vain to explain it only meant the last 5 chapters were being compiled into a volume...)
Light novel and manga adaptations don't always coincide, one recent strange example was Territory Management For The First Time, By The Adventurers Of Level 99/レベル99冒険者によるはじめての領地経営
The webnovel started in 2014 and is still ongoing, according to amazon it had a light novel version in 2014-2017 with 6 volumes total, however it only got a manga adaptation a few months back, with, I think, only two chapters out yet as of this date.