We cannot give explanations, which apply to every registrar.
By the way: Our explanations are also a kind of prediction. As we know, predictions are difficult - especially about the future
There are (at least) two kinds of domains: generic domains like .com and country code domains like .cn.
Generic domains:
There are no direct costs for the transfer, but one year of registration is added at every change of registrar.
Some registrars invoice the new year after the transfer, others at the start of the new period.
Country code domains:
Many country code domains follow the model which is described above.
Some country-code extensions have another model:
I call this model the model of “tabula rasa”: If you transfer a domain to another registrar, the domain starts a new life. You pay for the registration of the domain, a new period begins.
You lose the time, which has been paid by you or by another owner at the former registrar.
If you know, that this model is applied, you can save money by waiting and transferring your domain some days before the expiration date.
Attention: Some registries don’t permit transfers some weeks before the expiration date.
Hans-Peter Oswald
https://www.domainregistry.de/...