The Social Security COLA is based on the annual change in the CPI-W for the third quarter (July, August,September) year over year. That means for there to be a COLA in 2017 the CPI-W in the third quarter of 2016 must exceed that index for 2015.
The magic number for 2015 is 233.277
If you track the CPI-W number each month (released around the middle of the following month), you will be able to estimate the COLA for 2017, if any.

