Precision Nutrition's Weight Loss Calculator: Eat less? Move more? Here's what it really takes to reach your goals.

Precision Nutrition’s
Weight Loss Calculator
Eat less? Move more? Here's what it really takes to reach your goals.

By John Berardi, Ph.D.


This weight loss calculator (based on the NIH Body Weight Planner and adapted from research collected at the National Institute of Diabetes and Digestive and Kidney Diseases), 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 new Precision Nutrition Coaching 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 some help jumping fat-loss hurdles?

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… overwhelming, to say the least.

That’s why we work closely with Precision Nutrition Coaching clients to help them lose fat, get stronger, and improve their health… no matter what challenges they’re dealing with.

It’s also why we work with health, fitness and wellness professionals (through our Level 1 and Level 2 Certification programs) to teach them how to coach their own clients through the same challenges.

Interested in Precision Nutrition Coaching? Join the presale list; you’ll save up to 54% and secure a spot 24 hours early.

We’ll be opening up spots in our next Precision Nutrition Coaching on Wednesday, July 17th, 2019.

If you’re interested in coaching and want to find out more, I’d encourage you to join our presale list below. Being on the list gives you two special advantages.

  • You’ll pay less than everyone else. At Precision Nutrition we like to reward the most interested and motivated people because they always make the best clients. Join the presale list and you’ll save up to 54% off the general public price, which is the lowest price we’ve ever offered.
  • You’re more likely to get a spot. To give clients the personal care and attention they deserve, we only open up the program twice a year. Last time we opened registration, we sold out within minutes. By joining the presale list you’ll get the opportunity to register 24 hours before everyone else, increasing your chances of getting in.

If you’re ready to change your body, and your life, with help from the world’s best coaches, this is your chance.

[Note: If your health and fitness are already sorted out, but you’re interested in helping others, check out our Precision Nutrition Level 1 Certification program].


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

Spots open July 17th — don't miss out! Join the PN Coaching presale
list today.

If you're interested in Precision Nutrition Coaching, we strongly recommend you join the presale list below. Spots are limited and open just twice per year.

Choose your program below and we'll send you more info. Plus you'll get the chance to register 24 hours early and get our lowest price ever — up to 54% off the general price.