You need to make sure at each registrar. Most of them offer a one year extension with the transfer, but there are those that will charge a transfer fee AND a separate renewal fee. Those are the ones to avoid.
Same applies with what people refer to as "push". Some registrars will transfer a domain to another account for free and some will not. For example, 1and1 charges an "account transfer fee" to move a domain to another account. It is the same price as a domain renewal, and does NOT include any time extension.
Just read carefully before paying any "transfer fee". Registrars set their own fees.