Someone checked in on the 30th of December 2017 and then checked out on the 2nd of Jan 2018, which year are the nights going to be credited for? 2017? 2018? A mix?
December 30 and 31 will be credited to 2017. Anything from January 1 on will count toward 2018
My experience was that I got the stay credited to each year - up to 1/1 on the "old" year, after 1/1 on the "new" year.
I would have thought it is credited at the end of the stay..just like other stays.
Your "status" year is Jan 1 - Dec 31, so that's how the nights are credited. Does not matter because you are not credited in "stays" for elite night credits. Take for example you are a Gold Elite, have 72 nights, and a stay planned for Dec 30 - January 17. You will get current year credit for Dec 30 & 31 for a total of 74 nights, and would still be Gold. If it is this year, then you'd get 24 rollover nights into next year, have 16 nights from Jan 1-17 credited for next year from that same stay, be Gold going into next year, and need 10 more nights to retain your Gold status. Now, you may be "gifted" Platinum status because Marriott sees your length of stay and awards you Platinum status, but you technically would not have earned it.
Status is figured just like the Airlines. Jan 1 thru Dec 31 each “calendar” year. If someone flies a round trip leaving Dec 31,2017 & returning Jan 1,2018 then Dec 31 counts in 2017 to give them their 2018 status, whereas the Jan 1 flight counts in 2018 to give them their status in 2019!
What about the “stay”. Does this count as 2017 or 2018 stay? Stays make a difference in SPG world!
From your question, the SPG stay would count in 2017 - it is based on the date (year) of arrival/check-in:
"Stay Credits: You will be credited for your qualifying stays based on the year you arrive at the hotel. For example if you arrive on 12/31/17 and depart on 1/2/2018, staying at an qualified rate, you would receive 1 stay credit for 2017."
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