You are correct, August would not fall into Population 1. Population 1 spans September through December. August would fall into Population 2 where the encounter starts >= 4 months and < 8 months after the start of the measurement period. Per the CMS Blueprint, v 11, page 334, the formula for calculating the duration in months is as follows: Day (date 2) >= day (date 1) Duration (months) = (year (date 2) - year (date 1))*12 + (month (date 2) - (month date 1))   Using 1/1/2014 as the start of the measurement period (Date 1) and 8/1/2014 as Date 2: Duration in months = (2014-2014) *12 + (8 - 1) = 7   Please let us know if this does not address your concern.

Considering a 12 month measurement period for CMS160v4 IPP1, IPP2 & IPP3, it appears that the month of August will be left out since IPP1 has a window of <4 months to end of the measurement period. Let me know if this interpretation of v4 spec is incorrect