I'm currently going for 1800 calories and after losing a decent amount of weight initially, I feel I'm making fairly little progress (to be expected). It seems to me that I actually lose more weight when I go a bit over the limit, which leads me to believe I might be eating so little that my metabolism slows down.
From what I've read, the rule of thumb is 3500 calories = 1 lb of fat, so in a week, you want to run a 500 calorie deficit each day. That, and most of the online calorie estimators seemed to cluster around 2600 calories/day for "maintenance" for me, assuming a mostly sedentary lifestyle. So I came up with 2100 and that mostly worked.
It's important to "dial it in" though, by weighing yourself at the same time every day and keeping track of how much you've lost in a given week. At first I was doing 1800 calories per day and I was losing too much, so I bumped up my number up to 2100 and leveled off a bit.
Nowadays I'm doing 2600 per day and I'm coasting pretty well, maybe losing a tiny bit, but making up for it by blowing my budget on occasion. 2600 is very easy to hit though... I can still do fast food for lunch and have no problem making my budget so long as I don't overdo it too much.
You have to constrain calories somewhat while making sure not to lower the metabolic rate. You can do this by tracking resting body temperature and pulse rate. If you wake up in the morning and have a body temperature much below 98F, you need to eat more. You also want to maintain a resting pulse rate over 70 bpm. If these measures dip, you are probably going too low in carbs or protein.
The fact is, only quite slow fat loss is safe and sustainable. All the more reason to not get fat in the first place.
It is a bit hard though, when you look at your goals and see that it'll take you 50 weeks to get to your goal weight at your current rate.
But then you realize: even when you hit your goal weight, you're not done, so there should be no hurry to get there. Keeping track of what I eat is a lifestyle for me now, not just a diet.
It's just that, to "just eat less", you actually have to log everything you eat so that you can't lie to yourself and blow your calorie budget without knowing it. This is true IMO even if you're doing low-carb or any other kind of diet. Accountability and making it impossible to lie to yourself is key.
Personal anecdote follows:
I lost 50 lbs (220 -> 170 lbs at 6'2") by logging every single (non-zero-calorie) thing that passes my lips, and I've kept it off for over a year. I have no idea if the amount of willpower I have is typical, but I definitely couldn't have done it if I didn't log what I eat. My theory is that if you don't actually account for all the food you eat, you're more likely to slip out of good habits because you gradually lie to yourself more and more until you're consistently blowing your calorie budget without realizing it.
But I really have to log everything, no matter what, even when I overeat. I can never say to myself "I'm on vacation, I can skip a day" or "well I'm already way over my calorie budget, may as well stop logging." Even if I end up 1500 calories over budget, all the food I ate is right there in my log.
There's a couple of reasons why I think this works for me:
* If I log everything, then it's impossible to blow through 200-300 calories on a bagel without realizing it, because the act of logging it puts it in the front of my mind.
* So long as I log everything, I can allow myself to blow my budget now and again. But since it's logged, I know exactly how many calories I need to make up in the coming days. On a week-to-week and month-to-month basis I can make it all even out.
* Even though it's human nature to want to eat back all the calories you lost (and you will slip), there's nothing in human nature that's preventing you from logging it all. I may binge and overeat because my body's telling me to, but perhaps the next day when I realize I'm already 1500 calories over for the week because of yesterday, I'm better equipped to compensate for it and have a salad for lunch instead.
* Once you find the right number of calories, you can avoid under eating as well. For me I decided early I wanted to lose only 1 lb/week. So in the early months of my diet there was plenty of times where I was something like 600 calories under my daily budget, and I didn't feel like eating, but I forced myself to eat anyway. This throttled my weight loss, but I think it was a major factor in keeping it off... my brain never really went into the severe feast/famine recovery that made me yo-yo right back to my old weight.
The main downside of this plan though, is I have no exit strategy... I have my "maintenance level" of calories set on my logging app, and I really do plan to just log what I eat for the rest of my life. (I've been doing it for two years straight now.) It's completely automatic for me (I use the "Lose It!" app on my iPhone) so I don't even see it as a burden any more, but I know that as soon as I stop I'll slip back into my old habits and gain all my weight back.