If we are talking about generic TLDs (such as .com, .info, .agency, etc.), the remaining term that you have with your current registrar will not be lost, it gets carried over. In addition to that, your domain will be renewed for one year as part of the transfer.
Another important thing to mention is that if your domain expired with your old Registrar, and you renewed it with them, it is advisable not to transfer the domain within 60 days from the previous expiration date. Otherwise, an extra year will not be added to the domain name since the losing registrar revokes renewal in such cases.
When it comes to country-code extensions (.de, .uk, .es, etc.), each Registry may set its own rules regarding a domain transfer procedure, so if you need more details on that, please contact our Support Team, and we will gladly clear things up for you.