ROI Calculation?

Hello friends,
I want to know how we calculate ROI.

ROI (return on investment) is a simple mathematical equation. In terms of SEO:
Profit - (Money + Resources) / Time = ROI

More info at Wikipedia (where’s it’s referred to as Rate of Return):

Actually you can develop ROI for each keyword if you have tracking of conversion in place, that conversion no need to be actual sale but lead generation also can put it as estimate dollar value that you can see the value of each keyword and then you put more effort in.

Thanks for giving Very Useful & Effective Answer, I also Dont know about how to Extract ROI, Thanks Alot for Sharing such a Wonderful Info !