Daily Energy Requirements Calculator

This calculator estimates your daily energy requirements — the number of calories your body needs each day to maintain your current weight — based on your age, sex, height, weight, and activity level. You enter those personal details and select how active you are, and it returns your estimated maintenance calories using the Mifflin-St Jeor equation, the most widely accepted formula for healthy adults. The result is a starting point for weight management: eat at that level to maintain, below it to lose, above it to gain.

Formula

The calculator uses the Mifflin-St Jeor equation to find your basal metabolic rate (BMR), then multiplies it by an activity factor. The BMR formula is:

BMR = (10 × weight in kg) + (6.25 × height in cm) − (5 × age in years) + s

where s is 5 for men and −161 for women. The result is in kilocalories per day (kcal/day), the same unit as the “calories� on food labels. To get total daily energy expenditure (TDEE), multiply BMR by an activity factor:

• Sedentary (little or no exercise): × 1.2
• Lightly active (light exercise 1–3 days/week): × 1.375
• Moderately active (moderate exercise 3–5 days/week): × 1.55
• Very active (hard exercise 6–7 days/week): × 1.725
• Extra active (very hard exercise, physical job, or training twice a day): × 1.9

All inputs must be in metric units: weight in kilograms, height in centimeters, age in years. If you know your weight in pounds, divide by 2.2046 to get kilograms; if your height is in feet and inches, convert to centimeters (1 inch = 2.54 cm).

Worked Example

Take the default values: a 30-year-old man, 70 kg, 170 cm, moderately active.

1. Calculate BMR: (10 × 70) + (6.25 × 170) − (5 × 30) + 5 = 700 + 1062.5 − 150 + 5 = 1617.5 kcal/day.
2. Apply activity factor: 1617.5 × 1.55 = 2507.125 kcal/day.
3. Round to the nearest whole number: 2507 kcal/day.

That matches the calculator’s output for the defaults. The BMR line shows 1618 kcal/day, which is the energy your body would use at complete rest.

When to Use This Calculator

Use it when you want a personalized calorie target for weight maintenance, or as a baseline for weight loss or gain. It is most accurate for healthy, non-pregnant adults with a normal body composition. It is a common starting point for:

• Planning a balanced diet to maintain weight
• Setting a calorie deficit for weight loss (typically 300–500 kcal below maintenance)
• Setting a calorie surplus for muscle gain (typically 200–300 kcal above maintenance)
• Understanding how your energy needs change with age, weight, or activity

The result is an estimate, not a medical prescription. Individual variation can be 10% or more, so treat it as a reasonable starting number and adjust based on real-world changes in your weight over a few weeks.

How to Read the Result

The main number is your estimated total daily energy expenditure (TDEE) in kilocalories per day. That is the number of calories you need to eat to keep your weight exactly the same, assuming your activity level matches the category you selected. If you eat more, you will gain weight; if you eat less, you will lose weight. The second number, BMR, is what your body burns just to keep you alive — breathing, heartbeat, brain function — without any movement. Your actual calorie needs are always higher than BMR because you move, digest food, and maintain body temperature.

For weight loss, a common approach is to subtract 500 kcal/day from your TDEE, which theoretically produces about 0.5 kg (1 lb) of fat loss per week. For weight gain, add 300–500 kcal/day. These are general guidelines; your results will vary depending on adherence, metabolism, and body composition.

Common Mistakes and Limitations

The most frequent error is mixing units — entering pounds and inches without converting. The formula expects kilograms and centimeters, so always convert first. Another mistake is overestimating activity level. Most people who work at a desk and exercise 1–2 times a week fall into “lightly active,� not “moderately active.� Choosing a higher category will overestimate your needs and can stall weight loss.

The Mifflin-St Jeor equation is accurate for most healthy adults, but it has limitations. It was developed from a sample of mostly normal-weight individuals, so it may be less accurate for people with very high muscle mass (it underestimates) or severe obesity (it may overestimate). It is not designed for children, pregnant or breastfeeding women, or athletes with extreme training loads. For those groups, consult a healthcare provider or dietitian.

Also, the activity factors are broad averages. A 15-minute walk and a 2-hour run both count as “exercise,� but their energy costs are vastly different. For more precision, you could track your steps or use a fitness tracker, but the calculator gives a solid starting estimate.

Why the Mifflin-St Jeor Equation?

Several formulas estimate BMR, including the older Harris-Benedict equation and the Katch-McArdle formula (which uses lean body mass). The Mifflin-St Jeor equation was developed in 1990 and has been repeatedly shown to be more accurate in modern populations, which tend to have higher body fat percentages than people in the early 1900s. It is now the recommended standard in many clinical settings. The Katch-McArdle formula is more accurate for lean athletes because it uses body fat percentage, but that measurement is harder to obtain. For general use, Mifflin-St Jeor is the best balance of accuracy and simplicity.

Frequently Asked Questions

Is this the same as my “calories burned� on a fitness tracker?

Not exactly. Fitness trackers estimate your total daily burn using your heart rate and movement data, which can be more personalized but also prone to error. This calculator gives a static estimate based on your stats and self-reported activity. Both are estimates; the calculator is a good baseline, and the tracker can show daily variation.

How do I convert my weight from pounds to kilograms?

Divide your weight in pounds by 2.2046. For example, 150 lb ÷ 2.2046 = 68.04 kg. For height, convert feet and inches to total inches, then multiply by 2.54. For 5’10�, that’s (5×12 + 10) = 70 inches, then 70 × 2.54 = 177.8 cm.

Why did my result change when I entered the same numbers but selected a different activity level?

Because the activity factor multiplies your BMR. A higher activity level means you burn more calories each day, so your maintenance needs go up. The difference between “sedentary� and “extra active� can be 700–900 kcal/day for the same person.

Can I use this calculator if I am pregnant or breastfeeding?

The formula is not designed for pregnancy or lactation. Energy needs are significantly higher during these periods — typically an extra 300–500 kcal/day in the second and third trimesters, and about 500 kcal/day while breastfeeding. Consult your healthcare provider for personalized guidance.

How often should I recalculate?

Recalculate whenever your weight changes by more than 2–3 kg (5–7 lb), or if your activity level changes significantly. As you lose weight, your BMR decreases because you have less body mass to maintain, so your maintenance calories drop. Recalculating every 5 kg of weight change keeps your target accurate.

Is it safe to eat below my BMR?

Eating below your BMR is generally not recommended for long-term weight loss, as it can lead to muscle loss, fatigue, and nutrient deficiencies. A moderate deficit of 300–500 kcal below your TDEE is safer and more sustainable. Very low-calorie diets should only be done under medical supervision.

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in age | Age | years | 30 | 18
in sex | Sex | Male=5, Female=-161
in weight | Weight | kg | 70 | 30
in height | Height | cm | 170 | 120
sel activity | Activity level | Sedentary=1.2, Lightly active=1.375, Moderately active=1.55, Very active=1.725, Extra active=1.9
out calories | Daily energy requirement | kcal/day | ((10 * weight) + (6.25 * height) - (5 * age) + sex) * activity | 0
out bmr | Basal metabolic rate | kcal/day | (10 * weight) + (6.25 * height) - (5 * age) + sex | 0