If your domain name expired, then your site will show an advertisement page.
A WHOIS lookup will reveal that the domain expires in the future, but was updated a day after it renewed, and the Nameservers are changed. (The Nameservers will automatically revert back when the registration fee is paid.)
You have 29 days renewal period to pay for your domain name, keep & renew it at the regular price.
*Then another additional 30 days to keep & renew it in the redemption period but it will cost extra to renew depending on the domain extension during this period.
After which it then enters into a pending delete period of 5 days when you can no longer renew it and you risk losing the domain to another buyer.