Calorie Calculator
Daily energy estimate from age, sex, height, bodyweight and activity, with a lockable protein, fat and carbohydrate split. Not medical advice.
NHS guidance uses 2,500 kcal/day for an average man and 2,000 kcal/day for an average woman as broad guides, and notes needs vary by age, weight, height and exercise. The fat-loss option uses the NHS Better Health average guide of reducing intake by about 600 kcal/day. US guidance uses calorie needs that vary by age, sex, height, weight and physical activity. MedlinePlus / NIH describes cutting about 500 calories per day as a common starting point for weight loss; this tool uses -600 kcal/day as a conservative planning adjustment.
Methodology
Resting metabolic rate uses Mifflin-St Jeor: men = 10 × weight kg + 6.25 × height cm − 5 × age + 5; women = 10 × weight kg + 6.25 × height cm − 5 × age − 161. Maintenance energy is RMR × activity multiplier. Calories/kcals are nutrition-label equivalents here; kJ = kcal × 4.184. For fat loss, NHS Better Health uses about a 600 kcal/day reduction as an average guide, so that is the default adjustment here.For fat loss, MedlinePlus / NIH describes cutting about 500 calories per day as a common starting point; this tool keeps -600 kcal/day as a conservative planning adjustment. The custom goal adds or subtracts the kcal/day amount you enter, bounded to ±2,000 kcal/day. Macro energy uses protein 4 kcal/g, carbohydrate 4 kcal/g and fat 9 kcal/g. The default split is 30% protein, 25% fat and 45% carbohydrate; locked macros reserve calories first and the remaining unlocked macros rebalance.
How your calorie target is calculated (TDEE)
This is a TDEE calculator at heart: it estimates resting metabolic rate with the Mifflin-St Jeor equation — the best-validated of the common formulas — then multiplies by an activity factor to get total daily energy expenditure, and finally applies your goal adjustment. Every step is shown under "Show me the maths", because a calorie target you understand is one you can sanity-check.
Choosing a deficit or surplus that actually works
The default fat-loss adjustment (−600 kcal/day) follows the NHS Better Health average guideThe default fat-loss adjustment (−600 kcal/day) is a conservative planning figure in line with common US guidance of cutting ~500 kcal/day — enough for steady progress without the rebound risk of crash deficits. Muscle gain uses a modest +250 kcal/day: building tissue is slow, and bigger surpluses mostly add fat. The custom option exists for coached athletes who know their numbers.
Macros: protein first, then preference
The macro split defaults to 30% protein / 25% fat / 45% carbohydrate and lets you lock any macro in grams — lock protein at your training target (the protein calculator can give you one) and let carbs and fat rebalance around it. All estimates assume healthy adults; a registered dietitian beats any calculator for medical conditions.
Sources
- NHS — Understanding calories. Energy is measured in kilocalories (kcal) and kilojoules (kJ). link Dietary Guidelines for Americans 2020–2025 — nutrition guidance uses calories/kcal and kilojoules conversion context. link
- NHS Better Health — Calorie counting. Average adult guide: 2,500 kcal/day for men, 2,000 kcal/day for women, and about a 600 kcal/day reduction for weight loss. link MedlinePlus / NIH — weight-loss calorie context. Cutting about 500 calories per day is a common starting point; the tool uses -600 kcal/day as a conservative planning adjustment. link
- Mifflin MD et al. A new predictive equation for resting energy expenditure in healthy individuals. Am J Clin Nutr 1990. PubMed 2305711. link
- Scientific Advisory Committee on Nutrition — Dietary Reference Values for Energy, 2011. UK energy reference context. link Dietary Guidelines for Americans 2020–2025 — U.S. energy reference context and healthy dietary patterns. link
- National Academies / Institute of Medicine — Dietary Reference Intakes: acceptable macronutrient distribution ranges for adults. link
Frequently asked questions
Which calorie formula does this use? Which calorie formula does this use?
It uses the Mifflin-St Jeor equation to estimate resting metabolic rate from sex, age, height and bodyweight, then multiplies that by an activity level to estimate daily maintenance energy. It uses the Mifflin-St Jeor equation to estimate resting metabolic rate from sex, age, height and bodyweight, then multiplies that by an activity level to estimate daily maintenance energy.
Are calories and kcals different? Are calories and kcals different?
For food labels and nutrition planning, “calories” usually means kilocalories (kcal). NHS guidance says energy may also be shown in kilojoules (kJ), so this tool can show the same target as calories/kcal or convert it to kJ. For food labels and nutrition planning, “calories” usually means kilocalories (kcal). US nutrition guidance and Nutrition Facts labels use calories; this tool can also convert the same target to kilojoules (kJ).
How does the fat-loss setting relate to NHS guidance? How does the fat-loss setting relate to US guidance?
NHS Better Health gives an average weight-loss guide of reducing daily intake by about 600 kcal. This calculator applies that as the default fat-loss adjustment, while still personalising the starting point from age, sex, height, weight and activity. MedlinePlus / NIH describes cutting about 500 calories per day as a common starting point for weight loss. This calculator uses -600 kcal/day as a conservative planning adjustment, while still personalising the starting point from age, sex, height, weight and activity.
How accurate is the result? How accurate is the result?
It is an estimate, not a measurement. NHS guidance notes that calorie needs vary by age, weight, height and exercise. Tracking bodyweight trend, training output, appetite and adherence over two to four weeks is more useful than treating any equation as exact. It is an estimate, not a measurement. US guidance notes calorie needs depend on age, sex, height, weight and physical activity. Tracking bodyweight trend, training output, appetite and adherence over two to four weeks is more useful than treating any equation as exact.
How should I choose activity level? How should I choose activity level?
Choose the example that best matches your average week, not your hardest day. If unsure, pick the lower option and adjust from real-world progress. Choose the example that best matches your average week, not your hardest day. If unsure, pick the lower option and adjust from real-world progress.
What macro split should I use? What macro split should I use?
The default split is 30% protein, 25% fat and 45% carbohydrate. You can lock one or two macros in grams and the calculator rebalances the unlocked macros across the remaining calories. The default split is 30% protein, 25% fat and 45% carbohydrate. You can lock one or two macros in grams and the calculator rebalances the unlocked macros across the remaining calories.
What happens if I lock too many macros? What happens if I lock too many macros?
If locked protein, fat or carbohydrate grams already exceed your calorie target, the tool flags it and sets the remaining unlocked macros to zero. Unlock one macro or lower the locked grams. If locked protein, fat or carbohydrate grams already exceed your calorie target, the tool flags it and sets the remaining unlocked macros to zero. Unlock one macro or lower the locked grams.
Does this replace advice from a dietitian? Does this replace advice from a dietitian?
No. It is an educational planning tool only. If you are managing a medical condition, have a history of disordered eating, are pregnant or breastfeeding, or are under 18, speak to a GP or registered dietitian. No. It is an educational planning tool only. If you are managing a medical condition, have a history of disordered eating, are pregnant or breastfeeding, or are under 18, speak to a physician or registered dietitian.