In short: An expired SSL certificate makes browsers show a security warning. Renew it with your host or certificate tool (free certificates renew automatically when set up) and check the new expiry date.
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How to check the expiry date
Click the padlock in your browser, open the certificate details and read Valid until. Or use the free Kiplock SSL check, which shows the date, the issuer and the names the certificate covers.
How to renew
Free certificates from Let's Encrypt last 90 days and are meant to renew automatically. If yours did not, the usual cause is a stopped renewal job, a changed server setting, or a DNS change.
On most hosts (Vercel, Netlify, Cloudflare, shared hosting control panels) renewal is automatic, and you can trigger it from the dashboard. On your own server, run the renewal command of your tool, for example certbot renew, then reload the web server.
With a paid certificate, buy or renew it from the issuer, install the new files, and restart the server.
Stop it happening again
Turn on automatic renewal. Add a reminder a few weeks before expiry. Check that the certificate also covers the www version of your domain.
Free, no sign-up.
Check your SSL certificateCommon questions
How long does an SSL certificate last?
Public certificates are valid for a limited time, now well under two years and often 90 days. Renew before the date shown.
Does an expired certificate hurt SEO?
Yes. Visitors leave at the warning and search engines can stop showing the site until it is fixed.
Is the certificate free?
Free certificates from Let's Encrypt work for most sites.