How do I determine the inflation rate between two dates? Can I use the difference in consumer price index between the dates rather than a series of inflation rates?
Reason for the question: I am setting up a spreadsheet listing investments, the purchase price, and purchase date. I wanted to be able to calculate the real earnings if I sold today at todays price. Assuming my spread sheet can already pull the current price for a stock I could determine the real earnings if I also had the inflation from time of purchase to now.
For sanity, quarterly or monthly accuracy is all I really need.
I have found the FRED data, but I'm not sure how to turn the known inflation for a series of months into a single rate. And I do not know how to use consumer price index data.
This question seems related.