How to Calculate Your Calorie Needs

How Many Calories Do I Need?

Lost Horizon Images/ Getty Images

Every diet should start with basic questions about calories. To begin with, you should know how many calories you need each day.  It sounds simple, but depending on the method you use to get your number, you might get different answers.  So how do you know which number is right?

There are different ways to determine your caloric needs. You can get a quick estimate online or a more specific (and expensive) test performed in a lab. There are pros and cons to each method. The best method for you depends on your goals, how much money you want to spend, and your access to various health services.

Look at these five different methods for determining your caloric needs and evaluate the pros and cons for yourself.

Keep a Pre-Diet Food Journal

use a smart phone app as a food journal
Use a smartphone app to record calories. Rayes Collection/ Digital Vision/ Getty images

One of the simplest ways to determine your caloric needs is to keep a pre-diet food journal.  Before you start a weight loss program, take one week to evaluate your current caloric intake. Don't make any changes to your diet, just write down everything you eat and the number of calories in each food. You should do this at a time when your weight is stable and your daily activity is typical.

After a week of recording your food intake, add the total number of calories for each day and divide by seven to get an average daily caloric intake. This should provide a general guideline for the number of calories your body needs to maintain its current weight. To lose weight, you need to decrease that number by roughly 500-600 calories per day.

  • Pros: Inexpensive, reinforces good weight loss habits such as food journaling. Online or smartphone apps make this method simple to use.
  • Cons: Requires tedious recording and may not be accurate if you aren't specific about measuring and recording your food portions.

Use an Online Calorie Calculator

woman on computer
Cultura/ Subjects/ Getty Images

There are several easy-to-use online caloric needs calculators, like the one at These tools provide a quick and easy estimate of the number of calories you need to eat to lose weight. To get the most accurate number, you need to know your current weight, height and goal weight. You also need to assess your daily activity level.

The number generated from these calculators is usually based on the Harris-Benedict formula for determining basal metabolic rate (BMR). The formula is widely recognized by experts as a reasonable estimate for daily caloric need. However, it is only as accurate as the information you provide and the answer is based on general guidelines. Daily activity level, for example, varies widely from person to person and there is no way for a single formula to accurately predict the metabolic impact of your specific activity level.

  • Pros: Provides a fast answer, free to use
  • Cons: Only based on general guidelines and estimates

Perform Metabolic Testing

Echo/Getty Images

Many gyms and other health centers now provide metabolic testing for a fee. Metabolic testing measures the number of calories that your body burns at rest (RMR) and the number of fat and carbohydrate calories your body burns while exercising at various exercise intensities. As part of your metabolic assessment, many trainers will also provide a metabolic training plan that will help you to burn more fat calories during exercise so that you lose weight more effectively.

While this seems like the most accurate way to find out how many calories you need, there has been some criticism of this testing process. The accuracy of your test may depend on the quality of equipment used, how often it is calibrated and the skill level of the person doing the testing. The service can be expensive and may require a gym membership.

  • Pros: Results are personalized and based on your specific performance.
  • Cons: Expensive and not widely available and some say that results are not as accurate as advertised.

Wear an Activity Monitor


Activity monitors are essentially high-tech food and activity journals. The devices collect and interpret a wide variety of data on your smartphone or computer. The popular Fitbit Flex (pictured above with a Nokia Lumia) measures steps per day and exercise activity. When you log your meals, it also calculates your intake of calories, fat grams, carbohydrate grams and protein. To set up the plan, the program estimates the number of calories you need.

Most tracking devices are worn on the wrist - but there are several brands that now provide more versatile options. This is important because you need to wear the monitors consistently if you want to get an accurate estimate of your calorie needs. If you choose to invest in a monitor, learn more about all of the popular models to you can find that device that works best for you.

  • Pros: Convenient, easy to use and measures a number of different variables
  • Cons: Devices can be expensive ($100-200) and not all monitors track food intake.

Meet with a Registered Dietitian

Chris Fertnig/ Getty Images

A registered dietitian will work with you to determine the number of calories you need to eat to lose weight, and the proportion of carbohydrates, protein and fat. A good dietitian will also strategize with you to overcome the most common roadblocks that have prevented you from losing weight in the past.

Many physicians can provide referrals to a registered dietitian. In some cases, the service may be covered by insurance if you have health conditions that are affected by your weight. But every insurance plan is different, so check with your provider to get details.

  • Pros: Personalized, professional, face-to-face approach.
  • Cons: May be costly or inconvenient if not covered by insurance

The Bottom Line: What's Best for Me?

weigh yourself to lose weight
IAN HOOTON/ Science Photo Library/ Getty Images

If price and convenience are important factors for you, you should start with the cheapest and easiest way to calculate your caloric needs. Keep a pre-diet food journal and compare your result to the number you get when you use a free online calculator. You’ll get a good estimate of the number of calories you need to eat to lose weight.

Keep in mind though, that the success of your food journal, your calorie counting and ultimately of your ability to lose weight depends entirely on the accuracy of your recording. Make sure you measure specific serving sizes and avoid common calorie counting pitfalls.

If you record data properly, cut calories and still don't see the results you want, consider investing more money into one of the other methods. A registered dietitian or metabolic testing are good options for people who prefer face-to-face support and accountability.

Continue Reading