Starting from gangotri its 18kms.. if you want so it can be easily covered in one day but u can also stay in chirbhasa which is 4kms from gangotri(just incase you are coming out of any other trek) .. (Read More). keep your tents and food ready because you wouldn't find any resturants or hotels there.. even your phone will not work.. make sure u know the bitter truths of going into a glaciers.. so be ready for amazing experience.. the beginners may go with NIMS based in Uttarkashi.. they are the best..