Exclude posts from one or more categories from displaying on your home page http://wpsites.net/web-design/exclude-category-posts-page/

functions.php

add_action( 'pre_get_posts', 'exclude_category_posts' );
/**
* @author Brad Dalton - WP Sites
* @example http://wpsites.net/web-design/exclude-category-posts-page/
*/
function exclude_category_posts( $query ) {
if( $query->is_main_query() && $query->is_home() ) {
$query->set( 'cat', array( -27, -30 ) );
    }
}