INTSTARTCMC reports the century month code (CMC) for the first month the survey was fielded, according to the DHS Program website.
The contextual variables in IPUMS DHS use the month in INTSTARTCMC as the month of the survey start date. The related variable INTENDCMC reports the century month code for the last month the survey was fielded, according to the DHS Program website.
Century month codes (CMC) are calculated by multiplying by 12 the difference between the year of an event and 1900. The year 1900 was chosen as the reference period because all of the DHS-relevant events occurred during the twentieth or twenty-first centuries. The month of the event is added to the previous result.
CMC = (Year - 1900) * 12 + Month
For example, the CMC for June 2002 is:
CMC = (2002 - 1900) * 12 + 6 = 1230
In other words, 1,230 months have elapsed between January 1900 and June 2002. Starting with CMC figures, one can calculate the month and year using the following formulas:
Year = int( ( CMC minus 1 )/12 ) + 1900
[int(x) is the integer part of x]
Month = CMC - ( ( Year - 1900 ) * 12 )
The information above is based on "Online Guide to DHS Statistics" (Rutstein and Rojas, 2006). [URL omitted from DDI.].
The century month codes reported in INTSTARTCMC are calculated using the Gregorian calculator.