Does anyone believe that Buffett (arguably the greatest investor of all time) does more than back-of-the-envelope calculations when making investment decisions?
He barely knows how to use Excel and rarely touches a computer, so, think long and hard about that.
The complexity of the calculations he uses when making investments are limited.
Either he veers away from overly complicated businesses that he cannot value with his relatively simple methods or he figures out what kind of back-of-the-envelope calculation makes plenty of sense for the business he's considering.
If it takes a Masters or PhD caliber of person / knowledgee to arrive at your valuation, the market will definitely never look at it like you do. Most market participants can't think on those levels and will never be comfortable with your thought process, therefore.
I believe Buffett's purchase of Bank of America, despite the company's complexity, was based significantly on a back-of-the-envelope calculation that made a lot of sense...a la Bruce Berkowitz.
And, I believe Buffett is a heavy user of multiples (derived based on his experience)...Alice Schroeder has said that all Buffett wants to do is make a 10% pretax return on his investment with little risk, for example. In his younger days (when he had less capital to manage), it was probably 15-20% instead of 10%.