Methodology

Our Methodology: How WellCal's Fitness Calculators Work

Every number on WellCal comes from a published formula. This page shows the formulas behind our calculators, where they come from, and what they cannot tell you.

Reviewed by Usama Awan Last reviewed: October 10, 2026
13
Free Calculators
0
Sign-Ups Needed
1990
Calorie Formula Published
Oct 2026
Last Reviewed
Our Approach

We Show Where Every Number Comes From

Health numbers are easier to trust when you can check them. For each calculator we name the method, the source and the limits.

1
Published formulas first
Each calculator uses a formula from published research or health guidance, such as Mifflin-St Jeor for calories and WHO and CDC categories for BMI.
2
Honest about limits
Results are estimates, not diagnoses. Every tool explains what it can and cannot tell you.
3
Independent
WellCal is not affiliated with or endorsed by the CDC, WHO, Mayo Clinic, NHLBI, ACOG or the American Heart Association. No advertiser or product influences how a result is calculated.
4
Free and private
Every calculator is free with no sign-up and runs in your browser. Your numbers are not stored. Optional meal plans and ebooks are sold separately. Read our privacy policy.
5
Corrections welcome
If you spot a mistake, tell us on the contact page and we will review it.
How It Works

The Core Formulas, Explained Simply

Three formulas sit behind most fitness results on WellCal: calories, macros and BMI.

Cal
Calories (BMR and TDEE)
Men: 10 × kg + 6.25 × cm − 5 × age + 5
Women: same, but − 161
TDEE = BMR × activity (1.2 to 1.9)
Example: a 32-year-old man, 74 kg, 175 cm, moderately active has a BMR of 1,679 and a TDEE of 2,602 kcal. Source: Mifflin et al., 1990.
Use the Calorie Calculator →
Mac
Macros
Default split: 30% protein, 25% fat, 45% carbs
Protein 4 · Carbs 4 · Fat 9 kcal per gram
Example: at 2,602 kcal that is 195 g protein, 72 g fat and 293 g carbs. A fixed split can suit some body sizes better than others.
Use the Macro Calculator →
BMI
BMI
BMI = weight (kg) ÷ height (m)²
Adults: under 18.5 · 18.5 to 24.9 · 25 to 29.9 · 30+
Categories follow WHO and CDC adult guidance. BMI does not measure muscle or body fat, so it can overstate risk for muscular people.
Use the BMI Calculator →
Our Tools

Method at a Glance for Every Calculator

A short description of how each of our 13 calculators gets its result.

CalculatorMethod
BMI CalculatorWeight (kg) ÷ height (m)², with adult categories from WHO and CDC.
Calorie CalculatorMifflin-St Jeor equation for BMR, multiplied by an activity factor to get TDEE.
Macro CalculatorSplits your goal calories into protein, carbs and fat.
Protein CalculatorBody weight multiplied by a grams-per-kg amount based on activity and goal.
FFMI CalculatorFat-free mass (kg) ÷ height (m)², using your body fat percentage.
Water Intake CalculatorBody weight, activity and climate, checked against dietary reference intakes for water.
Sleep CalculatorCounts back or forward in whole 90-minute sleep cycles.
Fiber CalculatorRecommended daily fiber for your age and sex.
Body Age CalculatorA lifestyle score from sleep, exercise, stress and diet. An educational estimate, not a clinical test.
Pregnancy Due Date Calculator280 days (40 weeks) from the first day of your last period, following ACOG guidance.
Ovulation CalculatorEstimates ovulation about 14 days before your next period. Not a method of birth control.
Cholesterol Ratio CalculatorTotal cholesterol ÷ HDL cholesterol.
Diabetes Risk CalculatorA screening estimate from age, BMI, family history, blood pressure and activity. Not a diagnosis.
Limits

What Our Calculators Can and Cannot Do

What they can do
Give you a sensible starting estimate from published formulas, and explain in plain English what the number means and what to do next.
What they cannot do
Diagnose a condition, replace a doctor or dietitian, or account for your medical history, medications and body composition.
Safety limits: our calorie calculator is for adults aged 18 and over and never shows a daily target below 1,500 kcal for men or 1,200 kcal for women. Speak to a doctor or registered dietitian first if you are pregnant, under 18, living with diabetes or a heart condition, or have a history of disordered eating. Read our full medical disclaimer.
UA
Reviewed by Usama Awan

Our content is written by the WellCal Editorial Team and reviewed by Usama Awan. This page was last reviewed on October 10, 2026.

Found something that looks wrong? Send us a message on the contact page. We read every one.

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