Originally Posted by
winniejupp
hi, marriott does not go by rolling window. the upgrade to silver , gold , platinum after 10, 50, 75 nights only happnes per calendar year (1st Jan - 31st Dec)
The rolling 12 month window is undocumented; meaning you will not find any information about it on marriott.com or in literature from Marriott. It does exist as noted by hhoope01 in post #3 and Rewards_Guy (who works for Marriott) in post #7. Also see this thread,
Marriott Concierge: Does Marriott use a rolling qualification year?, and make special note of the response from Marriott Concierge (official Marriott lurker) in post # 23.