For those of you who have been doing this whole weight loss thing for a while, does the math really add up? As in, when you subtract your average calories eaten daily from your average daily output (exercise, lifestyle, basal rate), multiply that number x 7, then divide by 3500 does it give you your total weight loss for the week? And does that number line up with what the scale says?
Does it really work that neatly? Or am I the only one who obsesses over numbers like this?
I'm asking because I want to know what goals to set and how much work I need to plan on doing to reach them.

Yes, the math is probably accurate, but NO, it doesn't work that neatly. There is so much science behind the 3500 calorie = 1 pound that I am not going to even question that, but keep in mind that the number we associate with our calorie output (BMR, exercise, etc.) is nothing more than an estimate. You WILL drive yourself crazy if you mathematically determine what your weight loss will be because it will not be accurate (at least in the short term). Your body does funny things and you could eat and exercise one week and lose 3 or four pounds and eat and exercise EXACTLY the same the next week and lose nothing. For you own sanity, use the numbers to get a general idea of how much you should be eating and that is it. Then just let things happen and tweak your calorie intake depending on the results you are getting and the results you want.

Using a tool like FitDay, and getting it adjusted to fit me (age, weight, activity level), I've found that it pretty well does predict my weight loss over time. That is, if it says I need a difference of 400 calories a day between what I eat and what I burn to reach a certain goal, then the closer I stick to the 400 calorie difference, over time, the closer I come to that goal. But I almost never drop weight in a straight line, especially if I weigh every day. Sometimes I lose nothing in a week or even two, and then I'll suddenly drop 3 pounds. Like that.

Our bodies aren't really like machines--they are highly complex and they interact with the environment in ways much more involved than a simple equation.

The Weight Goals section of FitDay is what I use to set up a plan. I use the downloaded version.

Jay

That is a dream - what kind of food you eat, etc. has a part in how much you will lose. Carbs cause water retention, for example.

For me it averages out over time. But it's not so neat for so many reasons. Water fluctuations is one. Also, keep in mind that just because you have a deficit one day does not mean that you lose the fat in the fat cell right away. Our food has to be digested -- which takes longer than a day from beginning to end. Think about it, you have a big meal and the weight of that meal is in your body until it is digested and the waste excreted. Nutrients need to be absorbed. We don't lose fat until our body draws on those stores...

You can probably tell I'm not an expert. In fact, I'd love to really learn more about the process. But suffice it to say that weight loss is a complex process!

I've been "doing the math" nearly every time I've dieted since I started seeing the formulas in magazines when I was 12 years old (almost 30 years ago), and I think it's a great estimation tool, but expecting it to be an exact science that will give you absolute control over your body and the scale - well I think that can add a lot of unnecessary stress to your life.