Your level is based on your 12 month spend. Once you level up, your clock resets and you will have access to that level for 12 months from that day. For example if you spend £50 on Jan 1st 2024 and then £100 on Feb 1st 2024 (£150 total) you would level up to Level 2. You will be Level 2 until Feb 1st 2025. During this time you can still spend further to Level Up again (which will start another 12 month clock) or, if you spend nothing, you will drop down to Level 1 spend.