Originally posted by Paul Nicks
https://www.namepros.com/posts/5983413/
Each registrar is charged a full renewal by the registry on the day the domain expires. The registry then grants the registrar 45 days in which they can ask for a refund for that renewal, if the registrar waits until the full 45 days are up they are pretty much stuck with the name. So, each registrar has different rules around how long during that 45 day window they keep the name renewed, which I know causes some confusion.
For GoDaddy, starting on day 26 post-expiry we try to find a new owner for the name via our GD Auctions system (after many attempts to get the original registrant to renew it). Our auctions + closeout period lasts 15 days (day 41 post expiry) so we typically award the domain to the auction winner on day 42. On day 43 we take the domains we didn't find a new home for and request a refund from the registry.
We process through tens of thousands of domains each day, so there are inevitably slowdowns or delays in our processing that sometimes pushes the refunds back to day 44. These potential delays are why we timed it out to day 43 originally, so we'd have a little cushion prior to getting stuck with the domains on day 45.