How often should I re-test my website for accessibility?

At minimum, once a year, plus after any significant change — a redesign, a new feature, a platform migration, or a CMS update. Many organizations now pair continuous automated scanning with periodic manual audits rather than treating testing as a one-time project, since accessibility degrades as content changes. A full WCAG 2.1 AA audit that combines automated tools with manual assistive-technology testing is the standard the DOJ and most legal frameworks reference, so that's the bar to re-test against, not just an automated scan.