How This Calculator Works
The calculator moves through four steps: estimate your BMR, scale it up to TDEE using your activity level, adjust TDEE for your goal to get a daily calorie target, and split that target into grams of protein, carbohydrate, and fat.
1. Basal Metabolic Rate (BMR)
BMR is the number of calories your body burns at complete rest to maintain basic functions like breathing, circulation, and cell repair. By default this calculator uses the Mifflin-St Jeor equation:
Men: BMR = 10 × weight(kg) + 6.25 × height(cm) − 5 × age + 5
Women: BMR = 10 × weight(kg) + 6.25 × height(cm) − 5 × age − 161If you enter a body fat percentage, the calculator also computes BMR with the Katch-McArdle formula, which uses lean body mass instead of total weight and can be more accurate for people who know their body composition:
LBM = weight(kg) × (1 − body fat% / 100)
BMR = 370 + 21.6 × LBM(kg)2. Total Daily Energy Expenditure (TDEE)
TDEE scales BMR up by an activity multiplier to estimate total calories burned per day, including movement, exercise, and digestion:
TDEE = BMR × activity multiplier| Level | Description | Multiplier |
|---|---|---|
| Sedentary | Little or no exercise, desk job | ×1.20 |
| Light | Exercise 1–3 days/week | ×1.375 |
| Moderate | Exercise 3–5 days/week | ×1.55 |
| Active | Hard exercise 6–7 days/week | ×1.725 |
| Very Active | Daily hard training or physical job | ×1.90 |
3. Daily Calorie Target
To lose or gain weight, this calculator applies a daily deficit or surplus to TDEE based on an assumption of approximately 7,700 kcal per kilogram of body weight (roughly 3,500 kcal per pound), a commonly cited approximation in weight-management literature:
Daily deficit/surplus = (kg per week × 7,700) / 7
Target (loss) = TDEE − daily deficit
Target (gain) = TDEE + daily surplus
Target (maintain) = TDEE| Rate | Weekly change | Daily kcal |
|---|---|---|
| Mild | ≈0.25 kg (0.5 lb) / week | ≈275 kcal |
| Standard | ≈0.5 kg (1 lb) / week | ≈550 kcal |
| Aggressive | ≈1 kg (2 lb) / week | ≈1,100 kcal |
4. Macronutrient Breakdown
The calculator sets default percentage splits based on your goal (higher protein when cutting, more carbohydrate when maintaining or gaining), then converts each percentage of your calorie target into grams:
Protein (g) = (target kcal × protein%) / 4
Carbs (g) = (target kcal × carbs%) / 4
Fat (g) = (target kcal × fat%) / 9You can drag the sliders in the results panel to change the split; the other two macros rebalance automatically so the percentages always total 100%.
How to Use Your Results
Treat the calorie target as a starting point, not a fixed rule. Track your actual body weight for 2–3 weeks at your calculated target, using a consistent method (for example, first thing in the morning), and compare the trend to what the deficit or surplus predicted. If your real-world trend is consistently off by more than expected, adjust the target up or down by 100–150 kcal rather than switching activity levels or formulas.
If you're cutting calories from a higher baseline, consider phasing the deficit in over 1–2 weeks rather than dropping straight to the full target, which can make the adjustment easier to sustain. Prioritize hitting your protein target consistently, since protein is the macronutrient most linked to preserving muscle mass during a deficit and to satiety during any phase. Carbohydrate and fat grams have more flexibility — the sliders let you shift between them based on training demands, appetite, and personal preference without changing your total calorie target.
Frequently Asked Questions
How many calories should I eat a day to lose weight?
Most people lose weight steadily by eating 500 calories a day below their TDEE (Total Daily Energy Expenditure), which produces a loss of roughly 0.5 kg (about 1 lb) per week based on the 7,700-calorie-per-kilogram assumption used in this calculator. A smaller deficit of around 250 calories a day is a gentler pace of about 0.25 kg (0.5 lb) per week, while a deficit of 750–1,000 calories a day speeds loss to roughly 1 kg (2 lb) per week but is harder to sustain and more likely to reduce muscle mass and energy levels. Enter your details above and select a goal rate to see the specific calorie target calculated for your body.
What is the difference between BMR and TDEE?
BMR (Basal Metabolic Rate) is the number of calories your body burns at complete rest just to keep essential functions running, such as breathing, circulation, and cell repair. TDEE (Total Daily Energy Expenditure) takes BMR and multiplies it by an activity factor to account for movement, exercise, and digestion, giving the actual total number of calories you burn in a day. TDEE, not BMR, is the number that should be used as the baseline for setting a calorie target to lose, maintain, or gain weight.
How accurate is this calorie calculator?
The Mifflin-St Jeor equation used in this calculator is generally considered one of the more accurate predictive formulas for resting metabolic rate in the general population, typically landing within about 10% of values measured by indirect calorimetry for most adults. Individual metabolism can still vary due to genetics, muscle mass, hormones, and other factors that a formula cannot fully capture, so the result is a well-reasoned starting point rather than a lab measurement. The most reliable way to refine the number is to track your actual body weight over 2–3 weeks at a given calorie intake and adjust the target based on the real-world trend.
What macronutrient ratio is best for fat loss or muscle gain?
There is no single macronutrient ratio that outperforms all others for every person, but protein intake is the variable with the strongest evidence behind it: research on resistance-trained individuals generally supports 1.6–2.2 grams of protein per kilogram of body weight during a calorie deficit to help preserve lean muscle mass. Once protein is set, the remaining calories can be split between carbohydrates and fat based on personal preference, training performance, and appetite control, since both provide usable energy when total calories and protein are adequate. The macro sliders in the results panel let you test different carbohydrate-to-fat splits while keeping the total calorie target fixed.
Should I eat back the calories I burn from exercise?
It depends on whether your chosen activity level already accounts for your regular workouts. If you selected an activity level like Moderate or Active because it reflects your typical exercise routine, that routine is already built into your TDEE, and adding exercise calories on top of it will overestimate your target. If instead you chose a conservative activity level, such as Sedentary, because your daily life outside of workouts is inactive, it's reasonable to add back roughly half of the calories a fitness tracker reports for a workout, since these devices tend to overestimate calorie burn.
What formula does this calculator use to estimate BMR?
By default, this calculator uses the Mifflin-St Jeor equation: for men, BMR = 10 × weight in kilograms + 6.25 × height in centimeters − 5 × age in years + 5; for women, BMR = 10 × weight in kilograms + 6.25 × height in centimeters − 5 × age in years − 161. If you enter a body fat percentage, the calculator also shows the Katch-McArdle formula, BMR = 370 + 21.6 × lean body mass in kilograms, which can be more accurate for people who know their body composition since it accounts for muscle mass directly rather than estimating it from height, weight, age, and sex.
How do I choose the right activity level if I'm not sure?
Match your activity level to your typical week, not your best week: Sedentary means little or no structured exercise and a desk-based routine; Light means exercise 1–3 days a week; Moderate means exercise 3–5 days a week; Active means hard exercise 6–7 days a week; and Very Active means daily hard training or a physically demanding job on top of exercise. Most people overestimate how active they are, so if you're between two levels, it's generally more accurate to choose the lower one and adjust your calorie target later based on how your actual weight trends.
Can this calculator be used during pregnancy, breastfeeding, or for children?
No. The Mifflin-St Jeor and Katch-McArdle formulas used in this calculator were developed and validated on non-pregnant, non-breastfeeding adults, and they do not account for the additional energy needs of pregnancy, lactation, or growth in children and adolescents. Anyone who is pregnant, breastfeeding, under 18, or managing a medical condition that affects metabolism should get personalized calorie and nutrition guidance from a doctor or registered dietitian rather than relying on this or any general-purpose calculator.
Methodology & Sources
BMR is estimated using the Mifflin-St Jeor equation, first published by Mifflin MD, St Jeor ST, and colleagues in a 1990 paper on predictive equations for resting energy expenditure in healthy individuals, in the American Journal of Clinical Nutrition. When body fat percentage is supplied, the calculator also applies the Katch-McArdle formula, associated with exercise physiologists Frank Katch and William McArdle's body-composition-based work on resting metabolism.
Activity multipliers reflect commonly used TDEE activity factors found throughout sports-nutrition and dietetics practice. The energy-equivalence assumption of approximately 7,700 kcal per kilogram of body weight (about 3,500 kcal per pound) is a widely cited approximation in weight-management literature; it is a useful planning estimate rather than an exact conversion, since real-world energy balance is also affected by metabolic adaptation, water shifts, and changes in lean versus fat mass over time. The protein guidance referenced in this page's FAQ reflects general ranges discussed in sports-nutrition research on protein intake for exercising individuals, such as position statements published by sports nutrition professional bodies.
Disclaimer
This calculator provides a mathematical estimate based on established formulas and general assumptions — it is not medical advice and does not account for individual medical conditions, medications, or metabolic disorders. Consult a doctor or registered dietitian before making significant changes to your diet, especially if you are pregnant, breastfeeding, under 18, or managing a health condition.