Here’s How To Figure Out How Many Calories You Actually Need In A Day
How many times have you come across the phrase “based on a 2,000 calorie diet” on a nutrition facts label? It’s everywhere, and it’s led a lot of people to believe that it’s the magic number for calorie consumption for every human in the population. But that’s not how it works. It’s an average, a guideline, an estimating tool to help you make generally informed food shopping decisions. It isn’t an exact measurement for you specifically — but there is a way to find that number.
First things first, you have to think beyond your gender, height and weight. An Olympic athlete of your size is going to burn calories a lot differently than you, right? Right. You have to factor in something called your basal metabolic rate, which is just a fancy way of saying the amount of energy your body needs each day to perform its very basic and vital functions — not exercise, not commute by walking to work, but truly the bare minimum.
Luckily, there is an equation for that. It’s called the Harris-Benedict equation (which was modified by Mifflin and St Jeor in 1990), and it’s deemed the most accurate measurement option (without scientific intervention, that is) by the American Dietetic Association. See the equations for both men and women below.
BMR = 10 x weight (kg) + 6.25 x height (cm) – 5 x age (years) + 5
BMR = 10 x weight (kg) + 6.25 x height (cm) – 5 x age (years) – 161
Obviously, these take a little brainpower because we have to convert our dimensions into metric units and follow the proper order of operations (shoutout to algebra class). But we’ve got this.
Let’s take a 25-year-old woman who is 5 feet and 6 inches tall and weighs 150 pounds as an example. Her equation would be: 10 x 68.0389 kg + 6.25 x 167.64 cm – 5 x 25 – 161. Use a handy-dandy calculator, and you’ll find that makes her basal metabolic rate 1,442.139 calories. That’s what her body needs to get its jobs done (metabolism, cell regeneration and repair, etc.) each day.
Now, we get to add activity to the mix! Obviously, the amount of exercise you log each week plays into how many calories your body burns on the given days of your workouts, but it also impacts how efficiently your body burns energy in general. (Think back to our Olympic athlete comparison for a second.) Here’s how the exercise multipliers for your basal metabolic rate break down:
Little-to-no exercise = BMR x 1.2
1-3 days of exercise each week = BMR x 1.375
3-5 days of exercise each week = BMR x 1.55
6-7 days of exercise each week = BMR x 1.725
Two-a-days or extra heavy daily exercise = BMR x 1.9
So let’s say our woman from our BMR calculations consistently exercises four days a week. We would take her BMR of 1,442.139 calories and multiply it by 1.55 to arrive at a grand total of 2,235.315 calories. That’s how many calories she needs to consume in her daily diet to maintain her current weight. If she wants to ditch a couple of pounds, she would need to consume between her BMR and that final number to create a healthy deficit (don’t drop below your BMR, folks). And if she wants to add a couple pounds of lean muscle mass, she would need to consume more than that final number (in the form of healthy proteins and nutrients, of course).
Voilá! Sure, it’s not a simple, one-step math problem, but hey, we never said it would be. Sometimes, if you want accurate answers, you gotta work a little for them. And we think finding our personalized numbers (and redoing them as the different factors like weight and activity level change throughout our lives) is definitely worth it as opposed to blindly following a label of averages.