Hi Steve,
One way.
With your months 1 to 12 in column A and your data in column B
this formula may get you started =SLOPE(B1:B12,A1:A12)
A positive result is UP and a negative result is DOWN.
If you use =IF(SLOPE(B1:B12,A1:A12)>0,"UP","DOWN")
it will return up and down.
SLOPE returns the gadient of the linear regression trendline that
runs through your data.
To see a visual representation of this select your data A1:B12,
Insert>Chart, select XYscatter, click on the frame with the lines
and dots, then click on finish. Now in your chart right click on
one of your data points and select Add Trendline, select Linear
and OK.
Hopefully that should be enough to get you started. There are
other options depending on your needs, if you need help
exploring them post back with more detail of how your data
is setup and what you are trying to achieve.
HTH
Martin