SSL certificate errors explained: what they mean and how to fix them

An SSL (more precisely TLS) certificate proves that you are talking to the real website and lets your browser encrypt the connection. When something is wrong with it, browsers show a full-page warning such as “Your connection is not private”.

The common errors

• Certificate expired (NET::ERR_CERT_DATE_INVALID). The certificate is past its end date. This is the most common one, and it is nearly always the owner’s fault: the renewal did not happen.
• Name mismatch (NET::ERR_CERT_COMMON_NAME_INVALID). The certificate was issued for a different address, for example example.com but not www.example.com.
• Untrusted issuer (NET::ERR_CERT_AUTHORITY_INVALID). The certificate was self-signed, or the chain of certificates is incomplete.
• Wrong date on your device. If your clock is wrong, every certificate looks expired or not yet valid.
• Mixed content. The page uses https, but loads an image or script over http. The padlock disappears even though the certificate itself is fine.

If you are a visitor

Check that your device’s date and time are right. Then try another network, because public Wi-Fi and some security software can interfere. Do not click through the warning on a site where you enter a password or payment details. If the warning appears on a site you own, read on.

If you own the site

1. Find the expiry date. Check your site: the result shows the issuer, expiry date, and whether the certificate covers your address.
2. Renew or reinstall. Most hosts include free certificates that renew automatically. If yours did not, reinstall it in your hosting panel.
3. Cover every name. Make sure both the bare domain and the www version are on the certificate.
4. Install the full chain, not only the main certificate, so every browser trusts it.
5. Redirect http to https, and update any links that still use http to fix mixed content.

Never be surprised by an expiry

Certificates last from a few months to a year. Add your site to the watchlist: the dashboard shows how many days each certificate has left.

Related guides

• What is DNS propagation, and why does a change take time?
• What happens when a domain name expires?
• How siteupdown.com checks a website, and what the verdicts mean

Last updated 2 November 2026. Written by the siteupdown.com team. Spotted a mistake?

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