What is the Mifflin-St Jeor formula and why is it used?

The Mifflin-St Jeor equation (1990) is currently the most widely validated BMR formula for general adults. For men: BMR = 10 times weight (kg) + 6.25 times height (cm) minus 5 times age + 5. For women: BMR = 10 times weight (kg) + 6.25 times height (cm) minus 5 times age minus 161. Studies comparing multiple formulas consistently find Mifflin-St Jeor has the smallest average error versus measured metabolic rate.

What is TDEE and how is it calculated from BMR?

TDEE (Total Daily Energy Expenditure) is your BMR multiplied by an activity factor. The five standard activity multipliers are: Sedentary 1.2, Lightly Active 1.375, Moderately Active 1.55, Very Active 1.725, Extra Active 1.9. For example, a man with a BMR of 1,800 kcal at a Moderately Active level has a TDEE of 1,800 times 1.55 = 2,790 kcal per day.

How many calories do I need to gain muscle?

A calorie surplus of 250 to 500 kcal above your TDEE supports muscle growth. This calculator adds 300 kcal above maintenance for the Gain goal, producing roughly 0.1 to 0.2 kg of lean mass per week when combined with resistance training. Larger surpluses add more fat alongside muscle. Protein intake of at least 1.6 g per kg of body weight per day is essential for maximising muscle protein synthesis.

How accurate is a calorie intake calculator?

BMR formulas estimate within plus or minus 10 to 15 percent of measured resting metabolic rate for most adults. The activity multiplier introduces additional uncertainty since people tend to overestimate their activity level. Treat the output as a starting estimate. Track your actual weight weekly for 2 to 3 weeks, then adjust the calorie target by 100 to 200 kcal if results do not match expectations.

What are macros and how does the calculator split them?

Macros (macronutrients) are protein, carbohydrates, and fat. For the Lose goal, this calculator uses 35% protein, 35% carbs, 30% fat. For Maintain: 25% protein, 45% carbs, 30% fat. For Gain: 30% protein, 45% carbs, 25% fat. To convert calories to grams: protein 4 kcal per gram, carbs 4 kcal per gram, fat 9 kcal per gram. Higher protein allocations during a deficit help preserve lean muscle mass.

Does calorie need change as I lose or gain weight?

Yes. As your body weight decreases, your BMR decreases because there is less tissue to maintain. After losing 5 kg, recalculate your calorie target to avoid a plateau. Similarly, as you gain muscle (which is denser than fat), your BMR and TDEE both increase slightly. Recalculating every 4 to 6 weeks or every 3 to 5 kg of weight change keeps the target accurate.

Is there a minimum daily calorie intake?

This calculator enforces a floor of 1,200 kcal per day regardless of the calculation result. Eating below 1,200 kcal for extended periods risks nutrient deficiencies, metabolic adaptation, and muscle loss. The National Institutes of Health recommends not going below 800 kcal per day without medical supervision. For individuals with very low TDEE (petite, sedentary women), a small deficit may not be achievable while staying above 1,200 kcal.

How do I convert my calorie target into actual meals?

The per-meal field divides your daily target by three (three meals per day). For 1,800 kcal per day, each meal would contain about 600 kcal. If you eat 4 or 5 meals per day, divide your daily total by that number. For a 250 kcal snack, subtract it from the daily total first, then divide the remainder across meals. Consistent portion control over weeks matters more than hitting exact targets on any single day.

Calorie Intake Calculator

Q: How many calories should I eat per day to lose weight?

Subtract 500 kcal from your maintenance calories (TDEE) to lose approximately 0.5 kg per week. For a person with a TDEE of 2,200 kcal, eating 1,700 kcal per day creates the required deficit. Deficits larger than 1,000 kcal per day are not recommended without medical supervision as they increase muscle loss and nutritional deficiencies.

Q: What activity level should I choose?

Sedentary: desk job, walks very little, no planned exercise. Lightly Active: office job plus 1 to 3 days per week of exercise. Moderately Active: moderate exercise 3 to 5 days per week, or a moderately physical job. Very Active: hard training 6 to 7 days per week, such as competitive athletes. Extra Active: both a physically demanding job and daily hard training. Most people who go to the gym a few times per week are Lightly Active.

Find out exactly how many calories to eat each day based on your age, size, activity level, and whether you want to lose fat, maintain weight, or build muscle.

Weight70 kg

30 kg200 kg

Height175 cm

120 cm220 cm

Weight154 lb

66 lb440 lb

Height

ft in

Age30

yrs

15100

Activity Level

Maintenance Calories

—

Protein

—

Carbohydrates

—

Fat

—

BMR (at rest)

—

TDEE (maintenance)

—

Per Meal (3 meals)

—

🥗 What is a Calorie Intake Calculator?

A calorie intake calculator tells you exactly how many calories to eat per day based on your body stats, activity level, and specific goal. The core method is the Mifflin-St Jeor equation: a research-validated formula that estimates your Basal Metabolic Rate (BMR), the number of calories your body burns at complete rest just to maintain basic functions like breathing, circulation, and cell repair. Your BMR is then multiplied by an activity factor (1.2 to 1.9, depending on how physically active you are) to produce your TDEE (Total Daily Energy Expenditure), the number of calories you actually burn in a typical day. From there, your goal determines the adjustment: subtract 500 kcal for fat loss, add 300 kcal for muscle gain, or eat at TDEE for weight maintenance.

The three most common goals each require a different calorie target. For fat loss, a 500 kcal daily deficit from your maintenance level produces approximately 0.5 kg of fat loss per week, the rate most consistently recommended by sports dietitians for preserving muscle mass. For muscle building (lean bulk), a 250 to 500 kcal surplus above maintenance provides the energy needed for new tissue synthesis without excessive fat gain. For maintenance, eating at TDEE keeps body weight stable over time and is the correct baseline target for anyone primarily focused on body composition rather than scale weight. This calculator also outputs a macros breakdown (protein, carbohydrates, and fat in grams) and a per-meal estimate, making it easier to plan actual food choices around the calorie target.

A frequent misconception is that lower calories are always better for fat loss. Below approximately 1,200 kcal per day, the body starts catabolising muscle for energy, micronutrient deficiency becomes difficult to avoid, and the hormonal response to severe restriction can impair fat loss. Another common error is overestimating activity level, which inflates the TDEE estimate and causes a "deficit" that is actually maintenance. The activity multipliers in this calculator are based on self-reported activity categories, which most people apply too generously. If weight is not changing at the calculated intake, reducing the activity level one step and recalculating is usually the right first move.

This calculator uses NDB.format for consistent number presentation and enforces a 1,200 kcal minimum to prevent unrealistic targets. Use the Maintain goal to establish your baseline TDEE first, then switch to Lose or Gain to see the adjusted target. Recalculate every 4 to 6 weeks or after every 3 to 5 kg of weight change, since BMR changes as body composition shifts.

📐 Formula

Calorie Target = BMR × Activity Factor ± Goal Adjustment

BMR (men): 10 × weight(kg) + 6.25 × height(cm) − 5 × age + 5

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

Activity Factor: Sedentary 1.2 | Light 1.375 | Moderate 1.55 | Active 1.725 | Extra Active 1.9

Lose Weight: TDEE − 500 kcal ≈ 0.5 kg/week fat loss

Maintain: TDEE (no adjustment)

Gain Muscle: TDEE + 300 kcal (lean bulk surplus)

Macros: Protein 4 kcal/g | Carbs 4 kcal/g | Fat 9 kcal/g

📖 How to Use This Calculator

Steps

Select your goal - Choose Lose Weight, Maintain Weight, or Gain Muscle using the goal tabs at the top. This sets the calorie adjustment applied to your TDEE.

Enter your details - Select metric or imperial units, then enter your weight, height, and age using the sliders or number inputs. Choose male or female to apply the correct Mifflin-St Jeor constant.

Choose your activity level - Select the level that best matches your typical week. When in doubt, choose one level lower than you think, as most people overestimate their physical activity.

Click Calculate to see your calorie target - Your daily calorie intake appears as the primary result, along with a macros breakdown in grams and a per-meal estimate based on three meals per day.

💡 Example Calculations

Example 1 — 30-Year-Old Woman, Fat Loss Goal

A 30-year-old woman, 65 kg, 165 cm, Lightly Active. Goal: lose weight.

BMR (women) = 10 × 65 + 6.25 × 165 − 5 × 30 − 161 = 650 + 1,031.25 − 150 − 161 = 1,370 kcal

TDEE = 1,370 × 1.375 (Lightly Active) = 1,884 kcal/day

Fat loss target = 1,884 − 500 = 1,384 kcal/day. At 35% protein: 1,384 × 0.35 / 4 = 121 g protein/day.

Daily calorie target: 1,384 kcal (121g protein, 121g carbs, 46g fat)

Try this example →

Example 2 — 25-Year-Old Man, Muscle Gain Goal

A 25-year-old man, 80 kg, 180 cm, Very Active. Goal: gain muscle.

BMR (men) = 10 × 80 + 6.25 × 180 − 5 × 25 + 5 = 800 + 1,125 − 125 + 5 = 1,805 kcal

TDEE = 1,805 × 1.725 (Very Active) = 3,114 kcal/day

Gain target = 3,114 + 300 = 3,414 kcal/day. At 30% protein: 3,414 × 0.30 / 4 = 256 g protein/day.

Daily calorie target: 3,414 kcal (256g protein, 384g carbs, 95g fat)

Try this example →

Example 3 — 45-Year-Old Man, Maintenance

A 45-year-old man, 90 kg, 178 cm, Sedentary office worker. Goal: maintain weight.

BMR (men) = 10 × 90 + 6.25 × 178 − 5 × 45 + 5 = 900 + 1,112.5 − 225 + 5 = 1,793 kcal

TDEE = 1,793 × 1.2 (Sedentary) = 2,151 kcal/day

Maintenance target = TDEE = 2,151 kcal/day. Per meal (3 meals): 2,151 / 3 = 717 kcal per meal.

Daily calorie target: 2,151 kcal (538g carbs equiv, 717 kcal per meal)

Try this example →

❓ Frequently Asked Questions

How many calories should I eat per day to lose weight?+

Subtract 500 kcal from your maintenance TDEE to lose approximately 0.5 kg per week. For a person maintaining at 2,200 kcal, eating 1,700 kcal per day creates the required deficit. Losing 0.5 kg per week is widely recommended as it better preserves muscle mass compared to more aggressive deficits. Deficits above 750 to 1,000 kcal per day increase muscle loss risk and are difficult to sustain without medical supervision.

What is BMR and how is it different from TDEE?+

BMR (Basal Metabolic Rate) is the calories your body burns at complete rest, maintaining basic biological functions. TDEE (Total Daily Energy Expenditure) is BMR multiplied by an activity factor that accounts for all daily movement. BMR is the floor; TDEE is what you actually burn on a typical day. Eating at TDEE maintains your weight. BMR alone understates true calorie needs by 20 to 90% depending on activity level.

Is the Mifflin-St Jeor formula accurate?+

The Mifflin-St Jeor equation (1990) estimates BMR within plus or minus 10 to 15% for most adults when compared to indirect calorimetry (the gold standard). Multiple validation studies have found it outperforms the older Harris-Benedict equation in accuracy. It performs best for adults of average body composition. It underestimates BMR for very muscular individuals and overestimates for those with very high body fat percentages.

What activity level should I choose?+

Sedentary (1.2): desk job, very little walking, no planned exercise. Lightly Active (1.375): office job plus 1 to 3 gym sessions per week. Moderately Active (1.55): physically active work or 3 to 5 days of exercise per week. Very Active (1.725): hard training 6 to 7 days per week or construction-level physical work. Extra Active (1.9): both a physically demanding job and daily hard training. Research consistently shows that people overestimate activity level.

Why does the calculator show a macros breakdown?+

Macros (protein, carbs, fat) determine how your calorie target is filled by food. For fat loss, higher protein (35%) helps preserve lean muscle while in a deficit. For maintenance, a balanced 25% protein, 45% carbs, 30% fat split supports general health. For muscle gain, 30% protein provides sufficient amino acids for muscle protein synthesis. Converting calories to grams: protein 4 kcal per gram, carbs 4 kcal per gram, fat 9 kcal per gram.

What is a calorie surplus and how much is needed for muscle gain?+

A calorie surplus is any intake above TDEE. This calculator adds 300 kcal above maintenance for the Gain Muscle goal, which most research considers an optimal lean bulk surplus: enough to support muscle protein synthesis without excessive fat accumulation. Natural muscle gain is limited to approximately 0.1 to 0.25 kg per week for most trained individuals. Larger surpluses (500-plus kcal) produce faster weight gain but a higher proportion of that gain will be fat.

How do I use per-meal calories practically?+

The per-meal figure divides your daily target by three. For a 1,800 kcal daily target: each of three meals should average around 600 kcal. If you eat four or five smaller meals, divide the total by that number instead. For people who have a large dinner and smaller breakfast and lunch, you can weight the distribution differently, for example 25% breakfast, 30% lunch, 45% dinner. What matters most is the daily total across the full week, not hitting an exact figure at each sitting.

Does age affect how many calories I need?+

Yes. The Mifflin-St Jeor formula subtracts 5 kcal per year of age from BMR, reflecting the gradual decline in lean muscle mass and metabolic rate that occurs with aging. A 50-year-old at the same weight, height, and activity level as a 25-year-old will have a BMR roughly 125 kcal lower. This accounts for the common experience that maintaining a healthy weight becomes harder with age even without major lifestyle changes.

What is the minimum safe calorie intake?+

This calculator enforces a minimum of 1,200 kcal per day. Below this level, meeting micronutrient needs becomes very difficult on a balanced diet, and the body may increase muscle catabolism to meet energy demands. The National Institutes of Health does not recommend going below 800 kcal per day without medical supervision. Very-low-calorie diets (500 to 800 kcal) should only be undertaken under clinical supervision with medical monitoring.

Why is my weight not changing even though I am following my calorie target?+

The most common reasons: (1) activity level is overestimated, making the TDEE too high and turning the deficit into maintenance; (2) food portions are underestimated or tracking is inconsistent, common even with careful measuring; (3) water retention is masking fat loss, especially around the menstrual cycle or after high-sodium meals; (4) metabolic adaptation has reduced TDEE after weeks of dieting. Track body measurements (waist, hips) alongside scale weight and reassess calorie target after 3 to 4 weeks without progress.

How often should I recalculate my calorie intake?+

Recalculate every 4 to 6 weeks or after every 3 to 5 kg of weight change. As body weight decreases, BMR decreases, so your maintenance TDEE and deficit target both drop. Failing to recalculate is the most common reason fat loss stalls after initial progress. Athletes increasing training load should also recalculate their activity multiplier upward. The calculator takes less than a minute to run, so regular recalculation is easy to build into a weight management routine.

🔗 Related Calculators

📌 Quick Tips

💡Start with the Maintain goal to establish your baseline. Then switch to Lose or Gain to see the adjusted target. The difference between maintain and lose is always 500 kcal for this calculator, which produces roughly 0.5 kg per week of fat loss.

💡Protein intake is critical during a calorie deficit. This calculator allocates 35% of lose-weight calories to protein, which provides roughly 1.6 to 2.0 g per kg of body weight for most people. This helps preserve muscle mass while the body burns fat.

💡If your weight is not changing after 2 to 3 weeks at the calculated target, adjust by 100 to 200 kcal in the right direction. Individual metabolism varies, and the formula is an estimate. Real-world tracking is the calibration tool.

💡Activity level is the most common source of error. Most people who exercise 3 to 4 days per week are Lightly Active or Moderately Active, not Very Active. Very Active applies to athletes training hard 6 to 7 days per week.

💡Per-meal calories are calculated as total divided by three. If you eat four or five meals per day, divide your daily target by that number instead to get your per-meal target.