Very basic answer: Here is a calculator that can give you a rough estimate of how many calories you should eat based on your goals (gain weight, lose weight, stay the same weight).
First, let’s talk about what it means to say you ~should~ be eating a certain number of calories per day.
OK. So if you do want to figure out how many calories you should eat, a good place to start is by determining your basal metabolic rate, or BMR.
Here's the equation for men:
And here's the equation for women:
That's a lot of numbers, so here is a calculator that can figure out your BMR for you.
Once you figure out your BMR, you then want to figure out how many extra calories you use every day, based on how active you are.
Those are also a lot of numbers to look at again! But don't worry. Here is a calculator that will find your TEE for you.
It's the one we linked to all the way at the top.
Once you know how many calories you use each day, you should think about what your goals are.
If you want to gain weight, you should talk to your doctor or a registered dietitian about how to do it in a healthy and targeted way.
If your goal is to build muscle and bulk up, for instance, the macronutrients in the foods you're eating matter just as much as how many calories you're adding to your diet. Eating milkshakes all day every day will help you gain weight, but you won't feel very good as it's happening. (On a related note, you might find some helpful tips in this story: 11 Ways To Build Muscle And Lose Fat.)
And if you want to lose weight, a healthy way to do that is to aim for losing no more than 1 or 2 pounds a week.
This calculator can help you figure out how many calories you'll want to eat if you want to lose 1 or 2 pounds per week.
Again, it's the one we linked to at the very top.
NOW. Everything written above are very basic guidelines for how to determine your daily calories. But you should know: This is all based on ESTIMATES. Your mileage may vary, depending on a lot of stuff.
1. The BMR equation we mentioned above is just an estimate — so it's not going to be totally accurate for a lot of people.
2. BMR estimates also don't consider your body fat percentage, or if you've got a lot of muscles.
3. You can get a better, more personalized sense of how many calories you typically burn by tracking what you eat, how much you exercise, and how much you weigh.
4. It's really hard to eat less than 1,200 calories a day and still be healthy.
5. The general idea of counting calories also doesn't take into account the TYPE of food you're eating. And it matters.
6. Most people aren't great at knowing how many calories they eat on a regular basis, especially if they try to do it by memory.
7. Burning more calories is easier than you might expect, actually.
8. If your goal is to lose weight, there are other things that can make it REALLY hard.
9. You should also be aware of some other things that might impact your metabolism.
If you take up weight training, for instance, and you build up a lot of muscle and lose fat, you might not lose any weight at all but you'll be burning more calories throughout the day than you used to — thanks to those muscles.
And certain diseases can also raise or lower your metabolism. Thyroid disease, for instance: Overactive thyroid can raise your metabolism, and underactive thyroid can lower it.
It's also worth mentioning here that if you're trying all this stuff and still feeling confused about your results (or suspect that your metabolism is WAY lower than it should be, based on all the things we've covered here), you may want to see a specialist, like an endocrinologist, who might be able to measure your metabolic rate and run some other tests to see what's going on.
10. Bottom line: When it comes to having control over your weight (whether that's maintenance, gain, or loss), a LOT of stuff can have an impact.
This post has been updated for clarity.