Probably the most common questions on the site are about calories: Am I eating enough? Do I really have to eat that many? How many should I eat? What's BMR? What's maintenance? Etc.
So instead of typing the same thing over and over and over again ... here's the sticky version.
Ultimately weight loss is about calories in vs. calories out. You must burn more calories than you take in - in other words, create a calorie deficit - in order to lose weight. The easiest way to do that is to cut back on what you eat. However, you don't want to cut back too far - eating too few calories is not good either. Eating too few calories can cause a metabolic slow down that will stall out your weight loss (not permanently, but long enough to cause frustration). It can also make it harder to get in the necessary amounts of nutrition that you need to lose weight healthily.
The idea behind cutting calories is to eat as many as you can to keep your metabolism revved while cutting enough to see a reasonable loss each week.
Also, the number of calories you should eat is NOT the same for everyone. If someone tells you that you need to eat X number of calories without knowing your height, weight, and age, then they're just pulling a number out of thin air. And there's no way that someone who is 6' and weighs 250 lbs should be eating the same as someone who is 5'4' and weighs 160 lbs. That's like saying an SUV and a sub-compact should use the same amount of gas. It's just silly.
So how do you determine how many calories to eat?
The standard formula for determining your BMR is based on the Harris-Benedict equation, which is as follows:
For men:
66 + (13.7 x weight in kilos) + (5 x height in cm) - (6.8 x age in years)
For women:
655 + (9.6 X weight in kilos) + (1.8 X height in cm) - (4.7 X age in years).
(see notes below for conversions)
Remember that your BMR is not your maintenance calories. BMR (Basal Metabolic Rate) is the number of calories you'd burn if you did nothing but lie in bed all day and breathe. It's the number of calories you need to run the basic functions of your body; to keep your heart beating, your blood flowing, your lungs working, etc.
Once you've determined your BMR, you'll use an activity multiplier to figure out what your Maintenance calories are; that's the number of calories you need to get through your regular daily activities - things like getting up, showering, going to work, washing dishes, and all those other things that make up your daily life.
The official multipliers for activity are the same for men and women:
1. If you are sedentary (little or no exercise): BMR x 1.2
2. If you are lightly active (light exercise/sports 1-3 days/week): BMR x 1.375
3. If you are moderatetely active (moderate exercise/sports 3-5 days/week): BMR x 1.55
4. If you are very active (hard exercise/sports 6-7 days a week): BMR x 1.725
5. If you are extra active (very hard exercise/sports & physical job or 2x training): BMR x 1.9
The number that you get from using that multiplier is your MAINTENANCE CALORIES for your current weight.
In order to lose weight, you want to eat less than your maintenance. A good place to start is about 30% less than your maintenance. So subtract 30% from the figure you get and start there.
Keep in mind that calories are always an estimate. No one burns the exact same number of calories every single day. Sleeping in 10 minutes means you'll burn fewer calories. Walking to the bathroom 2x more during the day means you'll burn more calories. If you're hot or cold you'll burn a different amount of calories. If you eat more or less, you'll burn a different amount of calories. So don't obsess down to the exact number. Use the number you get from the calculations as a guideline - if after a few weeks you're not losing weight, drop another 200-300 calories and see what that gets you. Or add in a little more exercise to burn a few more calories.
And remember that as you lose weight, you need fewer calories - so what was your maintenance will begin to be too much. Keep an eye on your weight loss and if it begins to slow down (or if you've lost more than 10% of your bodyweight), try dropping your calories by about 200 (not much more) to keep things going.
That's it. That's all there is to calories - it's not really that hard or that complex.
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To get your weight in kilos, divide your weight in lbs by 2.2 - so someone who weighs 150 lbs will weigh 68.18 kilos
To get your height in centimeters, multiply your height in inches by 2.54 - so someone who is 5'4" (64 inches) will be 162.56 centimeters.
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Once you know your calorie level, it's a good idea to register for a free account at or to log your meals and make sure you are eating within your calorie range.
