Precision Nutrition's Weight Loss Calculator: Eat less and move's what it'll take to reach your goals. | Precision Nutrition

Precision Nutrition's
Weight Loss Calculator
Eat less and move more... here's what it'll take to reach your goals.

By John Berardi, Ph.D.


Based on data collected at the NIDDK (National Institute of Diabetes and Digestive and Kidney Diseases) and the NIH (National Institutes of Health), this weight loss calculator factors in how your metabolism really works to predict how long it’ll take to reach a particular weight loss goal.


It’s a question that comes up from clients all the time:

I’m tracking my calories in and calories out religiously… but I’m not losing as much weight as I should. Why isn’t my diet working?!?

Yes, conventional wisdom states that reducing your intake (or increasing your expenditure) by 500 calories a day should lead to about 1 pound of fat loss per week (500 calories a day x 7 days = 3500 calories a week = 1 pound).

But that conventional wisdom is wrong. As discussed in this article all about the myth of metabolic damage, the metabolism is adaptive. As you eat less, your metabolism slows, throwing off common assumptions about calorie balance.

This excellent weight loss calculator takes into account the adaptive nature of metabolism and gives more accurate information on how hard you’ll have to work (and how long it may take) to reach your goals.

Body Weight Planner
Starting Information
Physical Activity Level
% Uncertainty Range
% Calories from Carbs
Sodium Intake (mg/day)
% Body Fat
Resting Metabolic Rate
Simulation Options
Weight Goal
Goal Weight ({{weightUnitsRadioGroupLbl}})
I want to reach my goal in (# days)
OR select a date
I want to reach my goal by
Physical Activity Change (Optional)
Weight Change Phase
To reach my goal, I will change my physical activity by %
Goal Maintenance Phase
To maintain my goal, I will change my physical activity by %
Change your calories (intake) or activity (expenditure) to see how your weight will change.
Change 1
{{int1_gradulalRampField ? "Complete change on day" : "Change starts on day"}} with an intake of {{energyUnitsRadioGroup}}.
Change your physical activity by %
New Calories from Carbs (%)
New Sodium Intake (mg/day)
Change 2
{{int2_gradulalRampField ? "Complete change on day" : "Change starts on day"}} with an intake of {{energyUnitsRadioGroup}}.
Change your physical activity by %
New Calories from Carbs (%)
New Sodium Intake (mg/day)
In order to maintain your current weight, you should eat:

{{maintCalsField | number:0}}

To reach your goal of {{goalWeight}} {{weightUnitsRadioGroupLbl}} in {{goalTime}} days, you should eat:

{{goalCalsField | number:0}}

To maintain your goal of {{goalWeight}} {{weightUnitsRadioGroupLbl}}, you should eat:

{{goalMaintCalsField | number:0}}

At the end of {{simulationLengthField}} days, you would weight:


At the end of {{simulationLengthField}} days, your Body Fat % would be:


At the end of {{simulationLengthField}} days, your BMI would be:


Simulation Details
Length of Simulation (days)
Initial Weight ({{weightUnitsRadioGroupLbl}}):
Initial % Fat:
Initial BMI:
Final Weight ({{weightUnitsRadioGroupLbl}}):
Final % Fat:
Final BMI:
Click and drag to zoom Download Chart as Image

Note: As you play around, if you have questions about how to use the calculator, check out this video tutorial.

To understand why this calculator is so good, let’s use an example client: Vanessa. She’s 40 years old, 5′ 6″ tall, weighs 185 pounds, has a very low level of activity at work, and a moderate level of activity outside of work.

Based on this information, the calculator has determined that she needs around 2,445 calories per day to maintain her weight.

Let’s say Vanessa would like to lose 40 pounds in a sustainable way over the course of the next year, without doing much additional exercise.

The calculator suggests that she’ll need to reduce her food intake to around 1,770 calories per day. (That’s 675 calories fewer than required for maintenance).

If you were to do conventional calorie math, these numbers wouldn’t make sense.

A daily calorie deficit of 675 calories would lead to a deficit of 246,375 calories over the course of a year (675 calorie deficit x 365 days = 246,375 calories).

This would, theoretically, lead to a 70-pound weight loss for Vanessa (246,375 calorie deficit / 3,500 calories in 1 pound of weight = 70 pounds lost). But the body doesn’t work that way. Instead, Vanessa would lose about 40 pounds.

Why this very large disparity?

As mentioned above, the metabolism is adaptive. That’s why it’s important to make sure your expectations about weight loss and body change are in line with how the body actually works.

This calculator can help with that.

Want more help?

You’ve probably noticed that losing weight and keeping it off can sometimes feel complicated. Figuring out how much to eat, how much exercise to get, and how to make it all work within the context of your real life… impossible.

At Precision Nutrition, it’s our mission to help make the process easier… without complicated calorie counting, step tracking, and (sometimes) annoying math.

Women and men in our Precision Nutrition Coaching programs learn how to balance their food intake and activity levels to facilitate weight loss and health improvements in sustainable, long-term ways.

And fitness and health professionals in our Level 1 and Level 2 Certification programs learn how to help their clients do the same.

Coming Wednesday, April 5th.

If you’re a health and fitness pro and would like to learn more about becoming an elite, world-class nutrition and lifestyle coach, check out our Precision Nutrition Level 1 Certification program; it kicks off soon.

Important: Since we only take a limited number of students each time we offer the program, and it sells out every time, the best strategy is to add your name to our free presale list.

Getting on the list gives you the chance to sign up for the certification 24 hours before everyone else. Even better, you save over $200 on the cost of the program.

[Of course, if you’re already a student or graduate of the Level 1 Certification, check out our Level 2 Certification, an exclusive Master Class for elite trainers looking to perfect their nutrition knowledge and coaching techniques].


Click here to view the information sources referenced in this article.

Don't miss out. Get on the Precision Nutrition Level 1 Certification presale list today.

If you're interested in the Precision Nutrition Level 1 Certification, we strongly recommend you join the presale list below.

We'll send you more info about the program, and give you the chance to register 24 hours before everyone else. You'll also save over $200.