Unused points expire at the end of the use year unless you bank them. Banked points are good until the end of the next use year, and then if they are still not used, they expire. You may not bank those same points again.
For example, if you have an August use year:
Your 2004 points are good for stays between 8/1/2004 and 7/31/2005. If you bank those points, they must be used prior to 7/31/2006 or they expire.
You have until the end of the sixth month to bank up to 100% of your annual allotment of points. You have until the end of the 9th month to bank up to 50% and until the end of the 10th month to bank up to 25% of your total allotment. No banking is allowed in the last two months of your use year. If you have an August use year, your 100% deadline is January 31, the 50% is April 30 and the 25% deadline is May 31. If your deadline falls on a weekend or any other day that MS isnt open, you have to call earlier than the end of the month..
Banking is cumulative. Let's say you have 200 points. In month 5 you bank 75 points. In month 8, you'd like to bank more. Since you already have 75 in the bank, you would only be able to bank 25 more because you are in the 50% window. 75+25 =100, which is 50% of the total.
HTH.
Once points are in your account when do they expire... do you ever loose them if you don't use them? I read about the 6 month window to decide on using them or banking them Do points expire at some point in your account? Thanks 
