Calorie calculator
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- Formula shown below
- Reviewed
A calorie calculator estimates daily energy needs from the Mifflin-St Jeor equation, which sets basal metabolic rate at 10 × weight(kg) + 6.25 × height(cm) − 5 × age + 5 for men and − 161 for women, then multiplies by an activity factor. A 30-year-old man of 70 kg and 175 cm has a BMR of 1,649 kcal and needs about 2,556 kcal a day at moderate activity.
Result
Maintenance calories per day
2,556 kcal
BMR = 10w + 6.25h − 5a + k; TDEE = BMR × activity factor
- Basal metabolic rate
- 1,649 kcal
- Mild loss (−250 kcal)
- 2,306 kcal
- Steady loss (−500 kcal)
- 2,056 kcal
- Lean gain (+300 kcal)
- 2,856 kcal
A 30-year-old male weighing 70.0 kg at 175 cm has a basal metabolic rate of 1,649 kcal per day. At a moderate activity level (factor 1.550), total daily energy expenditure is 2,556 kcal, so eating about 2,056 kcal per day produces roughly 0.45 kg (1 lb) of weight loss per week.
Mifflin-St Jeor predicts the average for a population; individual metabolic rate varies by roughly ±10%. Treat the figure as a starting point and adjust against real weight change over two to three weeks.
How to use the calorie calculator
- 01
Enter your body measurements
Choose metric or imperial units, then type your current weight and height. Use a recent measurement rather than a remembered one.
- 02
Enter age and sex at birth
Age and sex are both terms in the equation. Metabolic rate declines with age and the sex constant differs by 166 kcal.
- 03
Choose your activity level
Select the multiplier matching your typical week. Most people overestimate here — choose the lower option when genuinely uncertain.
- 04
Read your maintenance figure
The result strip shows total daily energy expenditure. The rows beneath give targets for mild loss, steady loss and lean gain.
- 05
Verify against real change
Track weight for two to three weeks and adjust the intake target if actual change differs from the prediction.
The formula
BMR = 10w + 6.25h − 5a + k TDEE = BMR × activity factor
- BMR
- Basal metabolic rate in kilocalories per day — energy used at complete rest.
- w
- Body weight in kilograms.
- h
- Height in centimetres.
- a
- Age in years.
- k
- A sex constant: +5 for men, −161 for women.
- TDEE
- Total daily energy expenditure, including all activity.
- activity factor
- From 1.20 for sedentary to 1.90 for twice-daily training or heavy physical work.
The Mifflin-St Jeor equation was published in 1990 and is preferred over the older Harris-Benedict equation, which overestimates energy needs by roughly 5% in most modern populations. Katch-McArdle is more accurate still when a measured body fat percentage is available, since it works from lean mass.
Worked example
- Units
- Metric
- Weight
- 70 kg
- Height
- 175 cm
- Age
- 30
- Sex
- Male
- Activity level
- Moderate (×1.55)
- Result
- 2,556 kcal per day to maintain weight
Apply the male Mifflin-St Jeor equation: (10 × 70) + (6.25 × 175) − (5 × 30) + 5 = 700 + 1,093.75 − 150 + 5 = 1,648.75 kcal, rounding to 1,649 kcal of basal metabolic rate. Multiply by the moderate activity factor: 1,648.75 × 1.55 = 2,555.6 kcal per day for maintenance. A 500 kcal daily deficit gives roughly 2,056 kcal, which produces about 0.45 kg (1 lb) of loss per week, since a kilogram of body fat stores roughly 7,700 kcal.
Frequently asked questions
How many calories should I eat a day to lose weight?
A deficit of 500 kilocalories a day below maintenance produces roughly 0.45 kg (1 lb) of loss per week, because a kilogram of body fat stores approximately 7,700 kilocalories. Deficits above 1,000 kcal per day risk muscle loss and nutrient shortfall. Intake below 1,200 kcal for women or 1,500 kcal for men warrants medical supervision.
What is the difference between BMR and TDEE?
Basal metabolic rate is the energy the body uses at complete rest to sustain circulation, respiration, temperature and cell function — typically 60 to 70% of daily expenditure. Total daily energy expenditure adds the thermic effect of food, deliberate exercise, and non-exercise movement. TDEE is BMR multiplied by an activity factor between 1.20 and 1.90.
How accurate is the Mifflin-St Jeor equation?
Mifflin-St Jeor predicts measured resting energy expenditure within 10% for roughly 80% of non-obese adults, which makes it the most accurate of the widely used predictive equations. Individual variation of ±10% remains, so the figure is a starting estimate. Two to three weeks of tracked weight change is a more reliable guide than any equation.
Which activity multiplier should I choose?
Use 1.20 for a desk job with no deliberate exercise, 1.375 for light exercise one to three days a week, 1.55 for moderate exercise three to five days, 1.725 for hard exercise six or seven days, and 1.90 for a physically demanding job or twice-daily training. Self-reported activity is routinely overstated, so choose conservatively.
Do calorie needs fall with age?
Yes. The Mifflin-St Jeor equation subtracts 5 kilocalories per year of age, so a 60-year-old needs about 150 kcal per day less than a 30-year-old of identical size. Most of the real-world decline comes from lost muscle mass and reduced spontaneous movement rather than from age itself, which is why resistance training substantially blunts it.
Does a calorie deficit still work if metabolism adapts?
Metabolic adaptation is real but modest. Sustained restriction lowers energy expenditure by roughly 10 to 15% beyond what the smaller body size predicts, through reduced non-exercise movement and hormonal change. Energy balance still governs the outcome; the practical implication is that maintenance intake must be recalculated as weight falls.
How many calories are in a kilogram of body fat?
Approximately 7,700 kilocalories per kilogram, or 3,500 per pound. The figure comes from adipose tissue being about 87% lipid, with each gram of fat supplying 9 kilocalories. Early weight change is faster than this predicts because glycogen and its bound water are lost first, which is why the first fortnight tends to flatter a new deficit.
Sources
- A new predictive equation for resting energy expenditure in healthy individuals — Mifflin et al., American Journal of Clinical Nutrition, 1990
- Dietary Guidelines for Americans — estimated calorie needs — US Departments of Agriculture and Health and Human Services
- Healthy diet — energy intake fact sheet — World Health Organization
Last reviewed: · Formula and sources verified by Syed Aqeel Ahmad Gillani. See the methodology for how every calculation is derived.