As an Ultimate member, you are eligible for 1-month's free freeze within a 12-month period. Once you add the freeze, your membership will remain active up to your next payment date and then the freeze will begin. The freeze will automatically end at the end of that billing month.
You can remove the freeze before the month is up, but you will be asked to pay a pro-rata portion of your monthly membership when you unfreeze so you can use the gym again straight away.
When freezing your membership, please do so 5 working days before your next collection date to avoid being charged your regular monthly fee You may find this article helpful as an ultimate monthly member, can I freeze after the free freeze ends?