With CommuterClub, you will always make 11 payments in 12 months which means you effectively get one month of free travel.
For most members, this is at the end but depending on how your payments were spread out, it can also happen at the start or during your ticket.
In particular, if you joined in December there is a chance that you will have paid a bit ealier. That's because December is unique given the logistical challenges around Christmas and so we sometimes take payment a bit early since we want to make sure you get your ticket in time for the start date.
In that situation you would then get 3 weeks free in December and 1 week free in January. But it's still a month free overall!