If you didn’t have to calculate ROI for your email system then you shouldn’t have to calculate ROI for your performance management system - it’s just another part of every day business. If you absolutely must come up with some numbers though, here are a few things that might help.If you didn’t have to calculate ROI for your email system then you shouldn’t have to calculate ROI for your performance management system - it’s just another part of every day business. If you absolutely must come up with some numbers though, here are a few things that might help.