Calculating percentage increase and decrease

How do you calculate a percentage increase or decrease for one of your holdings (without using portfolio software you cheaters)? For some reason, I always have to look this one up. Apparently grade school math can fade a bit over time.

Something else that changes over time – the teachers get cuter. I dated a teacher recently and it was pretty strange to think about. Lecherous old man-dom here I come.

OK, back to the task at hand.

Let's use the example of needing to calculate the percentage increase of 11 to 21.

1. The first step is to find the difference between the two numbers: 21 – 11 = 10
2. Take the result of that and divide it by the original number: 10 / 11 = .90909091
3. Multiply this last number by 100. Voila! Your increase from 11 to 21 is 91%!

Personal Sell: Paychex Inc (PAYX): $40.07: 20060428

As much as it pained me to do so, I had to sell out of my shares in Paychex for reasons related to taxes. Basically, I had to pay the government before a refund check was scheduled to arrive and my only funds available were in my trading portfolio. I got pinched and I hate it. Shut up. I know I should keep a better reserve pile so I don't have to do this (it's just that I've always liked having as much money as possible really working for me at any given time).

This stock was the only stock left in my portfolio that I could sell and get long term capital gains treatment. Paychex was a good run for me, however, as my shares were purchased at $31.06 on February 25, 2005. This means I had a percentage increase of 29% in 14 months or so. Booyakasha.