Body Mass Index (BMI) is a widely used screening tool that estimates whether you are at a healthy weight for your height. While BMI doesn't directly measure body fat or account for muscle mass, it remains one of the fastest ways to identify potential weight-related health risks and set a starting point for nutrition planning. This calculator goes further — after calculating your BMI, it uses the Mifflin-St Jeor equation to estimate your Total Daily Energy Expenditure (TDEE) and translates that into personalised calorie targets and macro breakdowns based on exactly how much you exercise.
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BMI & Healthy Weight
See your BMI score, which category you fall into, your healthy target weight range (BMI 18.5–24.9), and how far you are from it.
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Calorie Targets by Activity
Calories are calculated using your TDEE — which changes significantly based on how often you work out. Compare all four activity levels side by side.
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Macro Breakdown
Get your daily protein, carbohydrate, fat and fibre targets in grams — adjusted for whether you're losing weight, maintaining, or building muscle.
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Key Micronutrients
General daily targets for water, sodium, calcium, iron and vitamin D — the nutrients most people miss regardless of calorie intake.
How We Calculate Your Calories
This tool uses the Mifflin-St Jeor equation — the most accurate BMR (Basal Metabolic Rate) formula for the general population, validated in multiple clinical studies.
- For men: BMR = (10 × weight kg) + (6.25 × height cm) − (5 × age) + 5
- For women: BMR = (10 × weight kg) + (6.25 × height cm) − (5 × age) − 161
- TDEE = BMR × activity multiplier (1.2 to 1.9 depending on exercise level)
- Weight loss = TDEE − 500 kcal (roughly 0.5 kg loss per week)
- Muscle gain = TDEE + 300 kcal (lean bulk to minimise fat gain)
The more you exercise, the higher your TDEE — which means you can eat more while still losing fat, or gain muscle faster without excess fat accumulation.
How to Use Your Macro Targets
Macronutrients are the three main nutrients your body uses for energy. Getting the right balance matters as much as total calorie intake.
- Protein (4 kcal/g): Builds and preserves muscle. Aim for 1.6–2.2 g per kg of bodyweight. Higher end if losing weight (to prevent muscle loss) or building muscle.
- Carbohydrates (4 kcal/g): Primary fuel for training and brain function. Not the enemy — timing and source matter more than total amount.
- Fats (9 kcal/g): Essential for hormones, brain health, and fat-soluble vitamins. Keep at 25–35% of calories, prioritising unsaturated fats.
- Fibre: Not a calorie source, but critical for gut health, satiety, and blood sugar regulation. Most people eat half the recommended amount.
Frequently Asked Questions
Is BMI accurate for everyone?
BMI is a useful population-level screening tool but has known limitations. It doesn't distinguish between muscle and fat, so highly muscular individuals (athletes, bodybuilders) may show a high BMI despite being very healthy. It also doesn't account for age-related changes in fat distribution. Use it as a starting point, not a definitive diagnosis.
How many calories should I eat to lose weight?
A safe, sustainable calorie deficit for weight loss is 300–500 kcal below your TDEE, which typically produces 0.3–0.5 kg of fat loss per week. Larger deficits are possible but increase the risk of muscle loss, fatigue, and metabolic adaptation. The more you exercise, the higher your TDEE — meaning you can eat more and still lose fat.
How much protein do I need per day?
Current evidence supports 1.6–2.2 g of protein per kg of bodyweight for people who exercise. For those losing weight, staying at the higher end (2.0–2.4 g/kg) helps preserve muscle mass during a calorie deficit. Sedentary adults need less — the RDA minimum is 0.8 g/kg — but most health-conscious people benefit from more.
What is TDEE and why does it matter?
TDEE (Total Daily Energy Expenditure) is the total number of calories your body burns in a day, including your base metabolism, physical activity, and the energy used to digest food. It's the most important number for nutrition planning — eating above TDEE leads to weight gain, below leads to loss. It changes as you gain muscle, lose fat, age, or change your activity level.
What is a healthy BMI for women vs men?
The standard healthy BMI range of 18.5–24.9 applies to both men and women by WHO classification. However, some research suggests that women naturally carry a slightly higher body fat percentage at the same BMI, and older adults may benefit from a slightly higher BMI (23–27) for bone density and longevity. Asian populations may have higher health risks at lower BMI thresholds.
How quickly can I reach my target weight?
A realistic and sustainable rate is 0.5–1.0 kg per week for weight loss, or 0.25–0.5 kg per week for muscle gain (lean bulk). Faster rates often result in muscle loss or fat regain. The timeline shown in the results above assumes a 500 kcal daily deficit or surplus and serves as a general estimate — individual results vary with adherence, metabolism, and training.