Ask the RD: Can I Trust Calorie Calculators?

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Calories matter for weight loss, but what if you’re getting different calorie goals from different online calorie calculators? How do you determine which is correct? Let’s go over how online calorie calculators work, and I’ll give you a few pointers to make your weight-loss journey more successful.


Online calculators like MyFitnessPal help you lose, maintain or gain weight by predicting how many calories you have to eat to keep your body weight the same. Additional calories are subtracted or added to depending on your weight goal — this is your daily calorie goal. The three perks of using an online calorie calculator are:

1. It’s Easy
Punch in your height, weight, age, gender, activity level and weight goal to get your daily calorie goal. The math is done for you

2. It’s Cheap
It’s free to create a MyFitnessPal account and get a personalized calorie goal.

3. It’s Convenient
Predicting how many calories you should eat is the “calories in” side of the equation. What about “calories out”? An online calorie calculator can conveniently adjust your daily calorie goal to be higher to account for a tough workout.

So, what’s the downside? You pointed it out. Calorie calculators estimate your daily calorie needs and the results will not be 100% accurate. There’s also variability between what you get from one online calculator versus another since they use different calorie prediction equations. Fun fact: There are a handful of calorie prediction equations and many of them are named after their founder such as Mifflin St. Jeor, Harris Benedict and Owen, to name a few.

With any online calorie calculator, you must be willing to accept a level of uncertainty. Still, it can feel frustrating if you’ve been following a recommended calorie goal but not seeing the results you want. Know that you can adjust your daily calorie goal within MyFitnessPal to better suit your needs. Let’s run through a primer on how your calorie goal is calculated, and I’ll give you a few pointers.


The first time you use MyFitnessPal can feel like a veritable crystal ball — enter your height, weight, gender, the first time you had birthday cake and … sha-bam! Your daily calorie goal. How did they come up with this?

The app uses the Mifflin St. Jeor equations to estimate your basal metabolic rate (BMR). Mifflin does a decent job of predicting BMR from just your height, weight, gender and age. The BMR is how many calories you’d burn if you did nothing but stayed horizontal and binge-watched Netflix for 24 hours straight. Clearly, you don’t do that so calories are added for activity. Calories are also subtracted if you’re trying to shed some weight.

Here are the top three factors that affect your calorie goal:

1. Activity Level
Refers to how active you are when you’re not at the gym and can be approximated by your job, which is where most of us spend our time. Generally, an office worker should select “not very active” and a construction worker should select “active.” If you’re unsure what your activity level is and want to be conservative, head over to Goals > Activity Level and change it to “not very active.”

2. Exercise
Refers to how long and intense your exercise regimen is. The default is you’ll get exercise calories back, but you can also choose not to track exercise. Upgrade to MyFitnessPal Premium, and you can track exercise but not have it affect your daily goal.

3. Weight Goal
Refers to how fast you want to gain or lose weight. The faster your desired weight loss, the lower your daily calorie goal. Go to Goals > Weekly Goal to change how quickly you want to reach your weight goal.

The biggest takeaway here is that all online calorie calculators give you a ballpark estimate. The question to ask yourself is: Do I need a calorie goal to be perfectly accurate to make better eating choices? It’s a case of “don’t let perfect stand in the way of good.”

You can track your weight regularly and troubleshoot your daily calorie goal to lose or gain weight at a comfortable pace. Hint: You can override the app and set a custom calorie goal by going to Goals > Calorie & Macronutrient Goals.


Maybe you’re still hung up on getting that daily calorie goal just right. The good news is there are alternatives to online calorie calculators. The bad news is these options aren’t as readily available.

The gold standard for estimating calorie needs is indirect calorimetry (IC), which tracks the amount of oxygen and carbon dioxide you breathe in or out. Hospitals use IC because they’re dealing with a very sick population. However, it isn’t very practical otherwise because IC requires expensive equipment (e.g., $10–20K) and the know-how to use said equipment.

More practical is to get a Bod Pod screening. This machine uses air to accurately predict your body composition (Think: fat versus lean mass). It uses body composition to calculate your energy needs. The upside is this is a more accurate estimate of your calorie needs, and you also get a report of your body fat percentage. You can get a Bod Pod assessment at an elite fitness center or university gym from $50–100.


The more accurate the calorie estimate in an app, the more it will cost you. But, getting accurate calorie estimates is barely half the battle. Once you have a trusted daily calorie goal, it still takes work to stick with it. Also, don’t just focus on the quantity of calories either. Choosing quality calories improves your weight-loss success and helps you build a better body. Luckily, MyFitnessPal isn’t just an online calorie calculator. It also has a huge database of millions of foods that’s freely available and a strong community of people who can help you learn more about good nutrition. This makes it a popular choice for people who want an easy way to track their food, weight and health.

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