Yeast's Influence on SG

While writing the recipe for a batch of stout, I predicted the SG to be about 1.075. I got this number by working off of (4.1 on FAQ 1-4 Answers @ Williams Brewing) which didn't have an estimate for the pound of lactose I added to the brew. Come brew day, as soon as I was tucking the carboy into the closet I realized I hadn't taken an SG reading. I know SG should be taken before pitching the yeast, but I was curious what to expect out of this beer. So I sanitized a wine thief and took a sample. The reading came out to 1.098!

Was my approach of predicting SG by such rough means the reason my prediction was off or was it the fact that I hadn't calculated lactose and yeast?

Well, 1 lbs of Lactose would have bumped your SG up about 6 points from 1.075. I have never made a milk/sweet stout so I have no idea how much to use. However, you can do the math. Wort does settle in weird ways though. If you don't have a thoroughly mixed wort your sample will not read correctly. It's not good to mix the beer up or slosh it around when it's fermenting so I think your sample was off. I wouldn't worry about it. Is this an extract batch? If you got a good boiling going the whole time and used the right amount of water with an extract batch your SG will pretty much be spot on.

Yeah it was an extract recipe. 9# of LME, about 2# of specialty grains, and 1# of lactose. Definitely designed to be a sweet stout. I planned on this being a big beer, but not *that* big. So I'm going to say you're right on the misread. Thanks