Answer by user3532758 for How To Add Interval 30 Days in Laravel (MYSQL)

This may not be the solution you would have preferred, (I do not know why your current query would not work and as @tadman suggested, I too suggest checking the produced query), but an alternative approach would be to try with query builder methods and Carbon date library that is shipped with Laravel.

$highlightProject = Project::whereBetween('end_date', [\Carbon\Carbon::today(), \Carbon\Carbon::today()->addDays(30)])->get();