Diet calculator: calories, macros, BMI and water
Enter your details to get a daily calorie target for your goal, a protein, carb and fat split, your BMI and a daily water estimate. Nothing is stored or sent anywhere; everything runs in your browser.
How your numbers are calculated
BMR (the calories you burn at rest) uses the Mifflin-St Jeor equation: 10 × weight (kg) + 6.25 × height (cm) − 5 × age, then +5 for men or −161 for women. TDEE multiplies BMR by an activity factor from 1.2 (sedentary) to 1.9 (very active).
For fat loss the tool subtracts 20% (or 10% for the gentle option); for muscle gain it adds 10%. Targets never drop below 1,200 kcal for women or 1,500 kcal for men. Protein is set at 1.6-2.0 g per kg depending on your goal, fat at 25% of calories, and carbohydrate fills the remainder.
Next steps
- Fat loss: read the calorie deficit guide.
- Higher protein: see the high-protein guide.
- Heart health: try the Mediterranean diet.
Frequently asked questions
How does the calorie calculator work?
It estimates your basal metabolic rate (BMR) with the Mifflin-St Jeor equation, multiplies it by an activity factor to get total daily energy expenditure (TDEE), then adjusts for your goal.
How accurate is it?
Equations are estimates and can be off by around 10%. Track your weight for two to three weeks and adjust calories up or down by 100-200 per day if needed.
What are macros?
Macros are the three main nutrients: protein, carbohydrate and fat. The calculator sets protein by body weight, fat at 25% of calories and fills the rest with carbohydrate.
Is BMI a good measure of health?
BMI is a quick screening number. It does not distinguish muscle from fat, so use it alongside waist measurement and how you feel.
Results are estimates for healthy adults aged 18 and over. This tool is not suitable for pregnancy, breastfeeding, or people with medical conditions. Consult a healthcare professional for personal advice.