Simon Willison’s Weblog

Most administrators will force users to change their password at regular intervals, typically every 30, 60 or 90 days. This imposes burdens on the user (who is likely to choose new passwords that are only minor variations of the old) and carries no real benefits as stolen passwords are generally exploited immediately. [...] Regular password changing harms rather than improves security, so avoid placing this burden on users. However, users must change their passwords on indication or suspicion of compromise.

UK National Cyber Security Centre