exclude category from home

exclude-cat.php

<?php

function mw_exclude_cat_from_home( $query ) {
	// this is the category ID(s) you want to exclude.
	$to_exclude = array( 3 );
	if ( $query->is_main_query() && $query->is_home() ) {
		$query->set( 'category__not_in', $to_exclude );
	}
}
add_action( 'pre_get_posts', 'mw_exclude_cat_from_home' );