This is one of those things I posted on the old blog a couple years ago and kept meaning to bring over to this new one. It is a simple Excel spreadsheet for estimating the deconvoluted mass of an intact protein. It certainly isn't perfect (+/-1000 Da?), but it is better than what you'll find if you Google "free protein deconvolution," which, last I checked, comes up with nothing. If you use it, I just ask that you aren't a jerk about it. ;)
You can download it from my personal bytebuckets account here.