WordPress has 2 inbuilt functionalities to get the site url:
site_url() will always be the location where you can reach the site by tacking on
/wp-adminon the end, while
home_url() would not reliably be this location. You can also get this same field by using
get_bloginfo( 'wpurl' ).
home_url() would be where you have set your homepage by setting General > Settings “Site Address (URL)” field. You can get this same field by using
get_bloginfo( 'url' ) as well.