Example of a relative date query from the WordPress codex. https://codex.wordpress.org/Class_Reference/WP_Query#Time_Parameters

wp-query-relative-date-codex.php

<?php /** NOTE: This is the example from the Codex, which think is BAD. **/

// Create a new filtering function that will add our where clause to the query
function filter_where( $where = '' ) {
    	// posts in the last 30 days (hardcoded)
	$where .= " AND post_date > '" . date('Y-m-d', strtotime('-30 days')) . "'";
	return $where;
}

//Requires immediate additiona and removal of the filter for intended use.
add_filter( 'posts_where', 'filter_where' );
$query = new WP_Query( $query_string );
remove_filter( 'posts_where', 'filter_where' );