Does it ever NOT work...?!?!?!?!

Most of the stuff here is accurate, so I hate to be a buzzkill about this, but one other point really needs to be mentioned.

People SUCK at estimating calorie intake, like really...we're bad. Even scientists have trouble with it, which is why there are so few studies with isocaloric intakes.

This isn't necessarily a bad thing, as you can work around these tendencies for error, but it's good information to have.

1) Remember that the formula's that calculate how much you need to lose weight (or maintain, or bulk) are just estimations, derived to be 'close' for as many people as possible. You still have to pay attention to what's going on and adjust as needed. Don't blindly eat X calories daily because the formula told you to. Pay attention to your results.

2) Body changes, particularly weight, are not linear. There's so much other stuff going on that it can be very difficult to gauge your progress. You really need to give it time, like a month or more, to get a reasonable baseline to start from. The sooner you do that the better off you'll be. Using one of the standard formulas is a good starting point; stick with it for 4 weeks and reasses. Adjust as needed and repeat. Be patient, it's a long process, but worth it.

3) The better your estimations, the better your results will be. Have an understanding of what the numbers you're plugging in mean, and always strive for the greatest level of accuracy possible. That chicken you just logged, did you just pick an entry that looked 'close enough' in the mfp database? Did you guess at the weight rather than use a scale? Did you include the oil you used to cook it? Are you putting in things like 3 hours of vigorous house cleaning which comes up as 15,000 calories when it was really more like 2 hours and you didn't even break a sweat? The little (and big) things matter, especially early on. As you get more comfortable in your routine you should become better able to sort of eyeball it, and know when you're on track or not. The adjustments you'll need to make in your routine will become smaller and smaller since you'll already be pretty much on point (the challenge then becomes consistency). You will still need to come back and reassess your estimations from time to time, but it does get easier, and 'work' eventually.

ETA based on previous post: even with weighing and tracking everything people are still prone to errors in estimated calorie intake. It happens, you still need to pay attention to results. While it might not be a problem if you've gained a couple after 2 weeks, after 6 or 8 though you need to change something.