If you want to start tracking how many calories you eat—whether for weight loss, weight gain, or just out of curiosity—here’s a primer. Tracking your calories or macros (or both) is pretty easy once you’ve gotten the hang of it, but getting started can be confusing. With the right tools and the right habits, however, you’ll be on top of your own personal calorie numbers in no time.
Calories are a measure of energy. The more exercise you do, for example, the more calories you need to fuel that activity. Everything you eat has a calorie number attached to it (whether it’s on a label or not). In general, we eat about the same number of calories we burn.
Amazingly, our bodies can keep us at a roughly steady weight by making us hungrier if we haven’t eaten enough calories today, or making us feel full if we’ve had a lot. That said, consistently eating less than you burn results in weight loss; eating more than you burn results in weight gain.
Macros are your macronutrients: fat, protein, and calories. These are the major components of our food, and they're where calories come from. (Water and alcohol are also technically macronutrients, but they aren't conventionally part of macro tracking.)
You would track macros if you want to be sure you're getting enough protein, if you're trying to get enough carbs for athletic fuel, or if you've gotten advice from a dietitian on fine-tuning the exact balance of where your calories come from. Calorie-tracking apps will generally also tell you how many grams of each macro you're getting with each meal and throughout the day.
Most of the time, you should eat roughly the same number of calories each day that your body burns. That number varies from person to person. A 4’9”, 100-pound woman who only does light exercise might burn 1,440 calories per day. A six-foot, 280-pound man who does heavy workouts twice a day might burn 4,309. Most of us are somewhere in between, in the 2,000 to 3,000 calorie range.
I discuss calorie burn a little more here. Even though food labels use a 2,000-calorie diet to calibrate their “daily values” of various nutrients, the truth is that we each burn a different number of calories, and most of us burn more than 2,000. (The average for adults was, years ago, calculated to be 2,350. The FDA ended up going with 2,000 in part because they thought a round number was easier to understand.)
So if you would like to lose weight, you’ll want to eat slightly less than you burn. If you want to gain weight—as many people do when they’re trying to gain muscle—you’ll want to eat more calories than you burn. A good rule of thumb is to subtract 200-500 calories per day from what you burn, and that will be a good number for weight loss. Do the opposite if you’re trying to gain.
You may think of burning calories in the context of exercise, but don't forget that you also burn calories just by existing. Our bodies need somewhere around 100 calories per hour just to keep our cells alive, brain cells firing, and blood pumping. So if your watch tells you that you burned 300 calories by going for a jog, that's in addition to the 2,000-ish that you burn throughout the day.
Now that you understand the logic, you just need a starting estimate of how many calories your body burns in a typical day. If you already track calories, you can probably figure this out by what you usually eat when your weight is stable. For example, if you eat about 2,300 on average, and you haven't been gaining or losing weight, your "maintenance calorie" number is 2,300. If you don't have a starting number, plug your information into a TDEE (total daily energy expenditure) calculator like the one at tdeecalculator.net. Remember that any calculated number is only an estimate, and ultimately you’ll find out whether it’s correct by noticing what happens to your weight when you eat that number.
If you use a Fitbit or other device that estimates your calorie burn each day, that's also a good place to get a starting number. Just remember that this is also an estimate, and could still be off by a few hundred calories in either direction.
The easiest way to get a calorie number for a food is to look at its label. Or if your food doesn’t have a label, search for the name of the food plus “calories” and pay attention to the serving size and the source of the information. For example, when I google “apple calories,” I get a result telling me that a medium apple, about 3 inches in diameter, is 95 calories. The source is given as the USDA, which maintains a database of common food items. Here’s the entry for apples. It defaults to a 100-gram serving, but you can change the “portion” dropdown to show you the medium apple.
When you’re eating at a restaurant, calorie counts are sometimes shown next to each food item. If they aren’t, check the restaurant’s website, or search the restaurant’s name plus “nutrition information.” Often there’s a PDF hidden somewhere on their website with a bunch of calorie counts—and, often, other information like protein and carbohydrate content. That said, there’s a simpler way that people usually use when tracking calories: You use a calorie tracking app.
There are tons of good (or at least not horrible) calorie tracking apps out there. Cronometer is my pick: It’s got all the features you need even in the free version, and it’s goal-neutral, so you can use it whether you’re trying to gain weight, lose weight, or neither.
The most popular calorie tracking app is probably MyFitnessPal, which is baffling because it’s easily the worst one out there. The calorie information is often inaccurate, the interface is pretty in-your-face about weight loss whether you’re interested in that or not, and basic features like the barcode scanner are only available in the paid version. We have a roundup of alternatives to MyFitnessPal here.
