Why do “.biz” and ".us” expiration dates seem one day shorter than they should be?
When you register a domain name, the expiration date is set by the company that runs the central registry for that domain name “suffix”.
Most of these companies set an expiration date that works like this: “As long as you renew your domain name before this date, it will not expire”. But the company that runs the “.biz” and “.us” suffixes, NeuLevel, instead sets an expiration date that works like this: “As long as you renew your domain name by the end of this date, it won't expire”.
For example, if you register a domain name on January 1 for a single year, most central registries will say “the domain name expires January 1”, meaning that you need to renew it before that date to be sure it doesn’t expire.
NeuLevel would instead say “the domain name expires December 31”, meaning that you can renew it any time on that date and it won’t expire.
There’s actually no practical difference between these two. In both cases, you need to renew the domain name before January 1 to avoid any potential problems. (In practice, it’s usually a bad idea to wait until the last minute, of course, because any unanticipated problems might mean that you miss the deadline.)