add_filter('the_content', 'zm_insert_content_after_chars_words'); function zm_insert_content_after_chars_words($content) { //Perform this operation when more than 1000 characters $enable_length = 1500; //Insert after the first</p>after 500 characters $after_character = 1500; if ( is_single() && strlen( $content ) > $enable_length ) { $before_content = substr( $content, 0, $after_character ); $after_content = substr($content, $after_character ); $after_content = explode( '</p>', $after_content ); $text='Text content'; array_splice( $after_content, 1, 0, $text ); $after_content = implode( '</p>', $after_content ); return $before_content . $ after_content; } else { return $content; } }