BMI, BMR, TDEE & Body Fat Explained

If you have ever tried to get fit, lose weight, or understand your body better, you have probably come across BMI, BMR, TDEE, and body fat percentage. They sound technical. They are not.

This guide explains each metric in plain English — what it measures, how it is calculated, what your number means, and which free tool gives you that number.

BMI — Body Mass Index

What it measures

BMI compares your body weight to your height. It does not measure fat directly, but it is a quick screening number used worldwide to flag potential weight-related health risks.

The formula

What your BMI means (adults aged 20+)

Below 18.5	Underweight
18.5 – 24.9	Healthy weight
25.0 – 29.9	Overweight
30.0 and above	Obese

BMI has real limitations. It does not account for muscle mass, bone density, or fat distribution. A muscular athlete may register as overweight on BMI. Use the BMI Calculator as one data point — not your only measure of health.

BMR — Basal Metabolic Rate

What it measures

BMR is the number of calories your body burns each day doing absolutely nothing — just to keep you alive. It covers breathing, circulation, cell repair, and temperature regulation. If you stayed in bed all day and did not move, your body would still burn your BMR in calories.

The formula (Mifflin-St Jeor)

Men: BMR = (10 × weight kg) + (6.25 × height cm) − (5 × age) + 5
Women: BMR = (10 × weight kg) + (6.25 × height cm) − (5 × age) − 161

Use the BMR Calculator to find your exact number. It is the foundation for all calorie planning.

TDEE — Total Daily Energy Expenditure

What it measures

TDEE is your BMR multiplied by your activity level. It is the number of calories you burn in a real day — including movement, exercise, and daily tasks. TDEE is the number you use for weight management:

• Eat at TDEE → maintain your current weight
• Eat below TDEE → lose weight
• Eat above TDEE → gain weight

Activity multipliers

Sedentary (desk job, little movement)	BMR × 1.2
Lightly active (1–3 days exercise per week)	BMR × 1.375
Moderately active (3–5 days exercise per week)	BMR × 1.55
Very active (6–7 days hard exercise)	BMR × 1.725
Extremely active (physical job + daily exercise)	BMR × 1.9

Use the TDEE Calculator to find your personalised daily target. Then pair it with the Calorie Calculator to plan your meals.

Body Fat Percentage

What it measures

Body fat percentage tells you what proportion of your total body weight is fat. Unlike BMI, it directly measures body composition. Two people with the same BMI can have very different body fat percentages depending on their muscle mass.

General healthy ranges (adults)

Category	Men	Women
Essential fat	2–5%	10–13%
Athletes	6–13%	14–20%
Fitness level	14–17%	21–24%
Acceptable range	18–24%	25–31%
Obese range	25% and above	32% and above

Use the Body Fat Calculator to estimate your percentage from simple body measurements using the US Navy circumference method.

How These Metrics Work Together

Think of them as layers of the same picture:

1. BMI — quick height/weight screen. Flags a potential concern.
2. Body Fat % — confirms whether a concern is excess fat or lean mass.
3. BMR — tells you your minimum calorie requirement.
4. TDEE — adds your activity level to find your real daily calorie need.
5. Calorie target — set above, at, or below TDEE depending on your goal.

Benchmark Against Your Ideal Weight

Once you know your BMI and body fat, it helps to benchmark against a healthy range. The Ideal Weight Calculator uses four medical formulas (Devine, Robinson, Miller, Hamwi) to give you a range rather than a single number — more realistic than a single target.

Using Macros to Hit Your Calorie Target

Once you know your TDEE, the Macro Calculator breaks your daily calorie target into protein, carbohydrate, and fat targets — making it much easier to follow a structured eating plan.

Common macro splits:

• Balanced: 30% protein / 40% carbs / 30% fat
• High protein (muscle building): 40% protein / 30% carbs / 30% fat
• Ketogenic: 10% carbs / 25% protein / 65% fat

Frequently Asked Questions

Is BMI still a useful measure?

Yes, as a population-level screening tool. At an individual level it has well-known limitations. Use it alongside body fat percentage for a more complete picture.

Can I have a healthy BMI but high body fat?

Yes. This is sometimes called "normal weight obesity." It is more common in people with low muscle mass. Body fat percentage will identify this where BMI misses it.

What is the difference between BMR and TDEE?

BMR is what you burn at rest. TDEE is what you burn in a real day, including physical activity. TDEE is always higher than BMR and is the number you use for calorie planning.

Your Health Metrics Toolkit

• BMI Calculator — height/weight screening
• BMR Calculator — resting calorie burn
• TDEE Calculator — total daily calorie need
• Body Fat Calculator — body composition estimate
• Ideal Weight Calculator — healthy weight range
• Calorie Calculator — daily calorie needs
• Macro Calculator — protein, carb, fat targets