Guides
The questions behind the numbers.
A calculator gives you a figure. These explain where it came from, how much to trust it, and what to do when it disagrees with the one you got somewhere else. Every guide cites its sources.
14 guides across 4 topics.
Working out your numbers
What the calculators are doing, which number to use, and why two sites can hand you different answers.
Guide
BMR vs TDEE: what's the difference?
BMR is what you burn at complete rest; TDEE is your whole day. Which number to use for a calorie target, and why they are never the same.
Read guideTDEE Calculator
Guide
Why do TDEE calculators give you different numbers?
Four reasons two calculators disagree by hundreds of calories for the same person, and how to tell which number to trust.
Read guideTDEE Calculator
Guide
How to choose your activity level honestly
Sedentary, lightly active or moderately active? Six real weeks mapped to real multipliers, plus what your daily step count actually translates to.
Read guideTDEE Calculator
Guide
What are maintenance calories?
Maintenance calories are the intake that holds your weight steady. How to estimate the number, and how to find your real one from the scale.
Read guideTDEE Calculator
Guide
Is TDEE different for women?
The equation changes by one number for women: 166 kcal at rest. Far less than most assume, and less than picking the wrong activity level costs you.
Read guideTDEE Calculator
Guide
Does your metabolism slow down with age?
Not in your thirties or forties. A 2021 Science study measured this properly, and the real answer is about muscle, not metabolism.
Read guideTDEE Calculator
Losing weight and reading the scale
Setting a deficit that works, and interpreting a number that moves for reasons that have nothing to do with fat.
Guide
How big a calorie deficit do you actually need?
What a calorie deficit is, the arithmetic behind losing 1 lb or 0.5 kg a week, and why the familiar 3,500-calorie rule overpromises.
Read guideCalorie Calculator
Guide
Is BMI accurate if you're muscular?
Why BMI reads muscle as excess weight, who it misclassifies, and what to look at alongside it when the number does not match the person.
Read guideBMI Calculator
Guide
Why does your weight change so much day to day?
Water, glycogen, food in transit and salt move the scale far more than fat does. What a normal daily swing looks like, and how to read the number properly.
Read guideCalorie Calculator
Guide
When is the best time to weigh yourself?
First thing in the morning, after the bathroom, before eating. Why that time wins, how often to step on, and how to read what you get.
Read guideBMI Calculator
Guide
Do you weigh more at night than in the morning?
Yes, usually by 1 to 2 kg (2 to 4 lb), and none of it is fat. The arithmetic of what you carry through a day, and where it goes overnight.
Read guideBMI Calculator
Turning calories into food
Getting from a calorie target to what actually goes on a plate.
Guide
How much protein do you need per day?
What the evidence says about daily protein for building muscle, why the benefit plateaus, and how that translates into grams for your body weight.
Read guideMacro Calculator
Guide
How should you split your macros?
The order matters, the ratio mostly does not. What two trials of 1,400 people found when they compared the popular macro splits directly.
Read guideMacro Calculator
Lifting and the gym floor
The arithmetic of the equipment itself: what the bar weighs, what goes on it, and how a lift is scored.
Health note
These guides explain how the calculations work. They are general information, not medical advice, and nothing here is a substitute for talking to a doctor or a registered dietitian about your own situation.
If you have a medical condition, are pregnant or breastfeeding, have a history of eating disorders, or are making a significant change to how you eat or train, consider speaking with a qualified healthcare professional.