Cold WX Altitude corrections
4% per 10 deg below ISA of the height above the elevation of the altimeter setting source.
Example.
Assume airport elevation 1000' & OAT = -2degress.
Approach minima = 1200' altitude. (200' AAL)
Therefore ISA deviation is -15.
Altitude correction = 1200 x 0.04 x 15/10 = 72'
Therefore an Indicted Altitude of 1272' = a True Altitude of 1200'
But sebxl has the simplest formula.
4 x 15 x 1200/1000 = 72'