You've probably heard of many eating plans revolving around calorie intake—from calorie counting, to calories in-calories out (CICO), to a low-calorie diet. But one principle of weight loss that has remained tried and true is staying in a calorie deficit, or when you expend more calories than you consume.

However, if you've never tried this method of weight loss before, it can be pretty overwhelming. Since calories are found in macronutrients (a.k.a. macros)—carbs, proteins, and fats—how do you decide which ones you should be eating and which ones you shouldn't be? How do you calculate the calorie content of different foods? And most importantly, how do you determine how many calories your body needs individually to stay in a calorie deficit?

Before you start to spiral, here are all the answers to your questions from nutrition experts.

Meet the experts: Keri Gans, RD, has more than 20 years of experience working as a registered dietitian nutritionist. She doesn't believe in diets but rather making small changes that will lead to lasting success, which is the topic of her book The Small Change Diet. She is also a certified yoga teacher.

Roxana Ehsani, RD, is a board-certified specialist in sports dietetics and a national media spokesperson for the Academy of Nutrition and Dietetics. She served as the sports performance dietitian for the Georgetown University’s division I athletic department, IMG Academy, and worked with multi-sport athletes at a private practice.

First, what is a calorie deficit?

Some basics: A calorie is a measurement of energy. The calories in food supply your body with the fuel you need to survive. When you eat food, it’s broken down by your body to release energy to be used right away or stored for later, depending on what you need at that moment.

Your body needs to take in a certain number of calories to maintain your weight, says Keri Gans, RD, the author of The Small Change Diet. And so, “a calorie deficit is when you consume fewer calories than your body requires to stay at its current weight,” she explains. If you take in fewer calories than your body needs, your body will turn to the calories you have stored up to burn for energy. As a result, you’ll lose weight.

Every person’s caloric needs and deficits are different and depend on a bunch of factors, like how much you exercise, your genes, your hormones, and your metabolism, notes Sonya Angelone, RD, a spokeswoman for the Academy of Nutrition and Dietetics.

And it can be challenging to create a calorie deficit in a healthy way. "For example, most people might not pick the correct total amount of calories to go off, then create too much of a restrictive calorie deficit for themselves to follow," says Roxana Ehsani, RD, LDN, a national media spokesperson for the Academy of Nutrition and Dietetics.

A woman may need 2,400 calories a day based on her height, weight, and training volume (a very active athlete), but thinks she only needs 1,800 calories per day to maintain her weight. But if she decides she wants to lose weight, she may create an even bigger calorie deficit and cut out 500 more calories, ending up with 1,300-calorie meal plan.

Sometimes it’s not as simple as calories in and calories out, Ehsani adds. Some people have underlying conditions, nutritional deficiencies, or are on certain medications that can make losing weight difficult and simply creating a calorie deficit doesn’t work for them.

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How much of a calorie deficit do you need to lose weight?

It can be a little complicated to figure out your exact calorie deficit but, in general, it’s thought that shaving 500 calories from your daily intake should lead to one pound of weight loss per week.

“The classic definition is based on the fact that one pound of fat contains 3,500 calories,” Angelone says. “If you eat 500 calories less than the amount you need to maintain your weight, you will lose one pound in a week.” If you want to lose two pounds a week, you might try a 1,000-calorie daily deficit. You just typically don’t want to cut any more calories than that. “Healthy weight loss is considered one to two pounds per week,” Gans notes.

A calorie deficit is when you consume fewer calories than your body requires to stay at its current weight.

You don’t necessarily have to drop 500 calories a day from your diet to lose weight, though. “Any deficit will lead to weight loss,” Angelone says. “It will just take more or less time, depending how great the deficit.”

Creating a calorie deficit isn't a perfect science, though. Your metabolism’s speed is a factor, along with the type of calories you take in, Angelone notes. (Some nutrients, like sugar, are used up more easily and quickly than fiber, she explains.) Your body also compensates for short-term calorie changes, temporarily raising your metabolism if you eat more for a few days, and lowering it if you eat less.

How do I figure out my calorie deficit for weight loss?

There are a lot of different ways to figure out an appropriate calorie deficit, and some are more accurate than others. There are different ways of calculating calorie needs, but Angelone says she usually uses the Harris-Benedict Equation, Mifflin-St Jeor Equation, or Katch-McArdle Formula with her clients. Here’s how to figure out your deficit in a few different ways.

With your doctor or nutritionist

Every practitioner has a slightly different approach. Angelone will take calculations based on body measurements like weight and height, along with exercise level. And Gans prefers a more low-key approach. “I try to leave math out of the equation and instead focus with my patient on making small changes that can naturally lead to weight loss,” she says.

But some practitioners may even send you for metabolic testing, which measures how many calories you burn at rest (like when you’re sitting around), to try to get an accurate number.

With a formula

There are several formulas out there to help you calculate your calorie needs, but a study published by the Journal of the Academy of Nutrition and Dietetics found that the Mifflin-St. Jeor equation is very accurate. This equation calculates your basal metabolic rate (BMR), which is the minimum number of calories your body burns at rest.

For women, the Mifflin-St. Jeor equation is: BMR = (10 x weight in kg) + (6.25 x height in cm) – (5 x age in years) – 161.

So, the BMR equation for, a 25-year-old woman who is 5'4" and weighs 150 pounds would be this: BMR= (10 x 68) + (6.25 x163) - (5 x 25) -161 = 1,413 calories

The Harris Benedict equation is often used for comparison. That equation is: BMR = 655.1 + (9.563 x weight in kg ) + (1.850 x height in cm) - ( 4.676 x age in years).

For the same 150-pound woman, the BMR using the Harris Benedict equation would be: BMR= 655.1 + (9.563 x 68) + (1.850 x 163) - ( 4.676 x 25) = 1,490 calories

The results are slightly different depending on which formula you use. And Angelone stresses, “This is still an estimate, since so many factors affect weight loss.”

With an online calculator

Don’t feel like doing the math? There are plenty of online calculators that can help. The National Institute of Health’s Body Weight Planner is a good one to try, Angelone says. It looks at your current weight and fitness level, along with your weight-loss goals, and helps map out how many calories you need to take in to lose the weight over the period of time you specify. A nice perk: It also tells you how many calories to aim for once you reach your goal weight to help maintain it.

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Okay, so now how do I actually achieve this calorie deficit?

There are a few different ways you can go about creating a calorie deficit and, ideally, you’d factor in a combo of all of these changes.

  • Do more strength training. Exercise, in general, can help burn more calories, but strength training helps to boost your body’s energy needs, increasing how many calories you burn at rest, Angelone says. Muscles “require calories or energy 24/7, so if you have more lean muscle mass, you will need more calories to maintain weight. Thus, you won’t have to cut back on foods as much to create a deficit,” she says.
  • Reduce your carb intake. Your body converts most carbohydrates in your body to sugar, and those calories are always absorbed or stored in your body for later use, Angelone says. Cutting back on your carbs means your body will store less away for the future.
  • Add more protein, fiber, and healthy fat to your diet. “Build your meals with high-fiber foods, such as fruits and veggies, so you are still satisfied even though your entree size may be smaller than you are used to,” Gans says. Adding more fiber, protein, and healthy fat to your meals will “help you stay satisfied longer and help you eat less,” Angelone adds.
  • Stop eating after dinner. This is usually the best way to get a deficit, per Angelone. “Most people have met their calorie needs by then, so eating after dinner or before bed just adds extra calories,” she says.
  • Keep a food journal. Yeah, you’ve heard it before, but it actually works. Writing down what you eat on a regular basis can be eye-opening, and can also help you plan where you can cut back. “Just monitor the amount eaten,” Angelone says. “Decrease it slightly from there to avoid getting too hungry, then overeating later.”
  • Use an app. Ehsani is a fan of the MyPlate Calorie Counter app, which has a feature called Get Your MyPlate Plan, which helps you figure out how many calories you need per day, then gives you examples of how many servings worth of major food groups you need every day.

I’ve been doing a calorie deficit and working out for a while, but why am I not losing weight?

If you've been putting in the effort but not seeing results, it could be because of a few reasons.

  • You have an underlying condition you're not aware of. "There could be an underlying health condition that hasn’t been treated or detected yet that may make it more difficult for you to lose weight," says Ehsani. For example, an thyroid or hormonal issue could hinder weight loss. Getting regular checkups will help you catch these conditions.
  • You're not sleeping enough. "Let’s say you have been eating healthy, sticking to your calorie deficit, and started an exercise routine, but your sleep schedule has been suffering," says Ehsani. "Lack of sleep may be the culprit when it comes to not seeing any changes on the scale." Researchers found that people who sleep less typically consume more calories and crave high calorie foods. So make sure you are getting at least seven to nine hours a night. "Sufficient sleep also better regulates your body’s appetite regulating hormones," Ehsani adds.
  • You aren’t following the right calorie deficit. "You may just guess a number, then create your own calorie deficit from there, but this could lead to a restrictive diet and may set you up for failure and unrealistic and unattainable calorie amounts," says Ehsani. "You might see weight loss at first but then hit a plateau and your energy levels start to diminish, metabolism slows." It's best to meet with a professional first to determine how many calories your body truly needs, then get help deciding how many calories you should cut out to reach a calorie deficit in a healthy way.