There's both a matlab/octave and excel calculator available.

CRI2012 calculator, please cite: Smet KAG, Schanda J, Whitehead L, Luo RM. CRI2012: A proposal for updating the CIE colour rendering index. Lighting Research and Technology 2013;45(6):689-709.

Note: to download an uncorrupted CRI2012.p file: click on the file and on the page that opens click 'download'.