Qualification for tiers is based on a rolling 4-week Dream Car Competition cycle. Your Supercharged tier is calculated on a weekly basis after the Dream Car Competition has ended each Sunday night by considering your spend in the previous 4 weeks. Please note, it may take until 6am on a Monday morning for your tier status to be reflected in your account.
You can see the competitions that contribute to your Supercharged tier status on the My Supercharged Status page. Any spend in the current competition will count towards your Supercharged tier in the next competition.