Understanding your calorie results
Your three numbers fit together: BMR is the resting baseline, TDEE adds activity, and the target applies your goal. The activity factors follow the standard TDEE convention.
| Activity level | Multiplier | Typical description |
|---|---|---|
| Sedentary | 1.2 | Desk-based day with little or no deliberate exercise |
| Lightly active | 1.375 | Light exercise or sport 1–3 days per week |
| Moderately active | 1.55 | Moderate exercise or sport 3–5 days per week |
| Very active | 1.725 | Hard exercise or sport 6–7 days per week |
| Extra active | 1.9 | Very hard daily training or a physically demanding job |
- Prediction equations estimate population averages; an individual's measured resting metabolism commonly differs from the Mifflin-St Jeor estimate, and the equation is less validated at extremes of age, body size and in athletic or clinical populations.
- The 1200/1500 kcal floors are commonly used practical minimums for unsupervised dieting; clinical guidelines (for example the NIH/NHLBI obesity guidelines) place lower-calorie regimens in the medically supervised category.
- Energy expenditure adapts as weight changes — a target that produced steady change initially may need recalculating after significant weight loss or gain.
- Calorie targets are educational estimates, not medical advice; people with diabetes, eating-disorder history, pregnancy or other medical circumstances should set intake goals with a healthcare professional or registered dietitian.
How many calories should you eat per day?
Daily calorie needs are the energy required to run the body's basic functions plus the energy spent on movement and digestion. The largest share is the basal metabolic rate (BMR) — the calories burned at complete rest to power breathing, circulation, cell maintenance and brain activity. Multiplying BMR by an activity factor gives total daily energy expenditure (TDEE), also called maintenance calories: the intake at which body weight is expected to stay roughly stable.
This calculator estimates BMR with the Mifflin-St Jeor equation, published in 1990 in the American Journal of Clinical Nutrition. A systematic review by Frankenfield and colleagues for the American Dietetic Association (2005) found Mifflin-St Jeor to be the most reliable of the common prediction equations in healthy adults, which is why it has largely replaced the older Harris-Benedict formula in practice. Like all prediction equations, it estimates a population average; measured metabolic rates for individuals commonly differ from the prediction by several percent in either direction.
Health agencies frame weight change around gradual, sustainable adjustments. The CDC describes gradual weight loss of about 1 to 2 pounds (roughly 0.5 to 1 kg) per week as more likely to be maintained than rapid loss, which is the basis for the moderate 250–500 kcal/day adjustments used here. This tool never displays weight-loss targets below 1200 kcal/day for women or 1500 kcal/day for men: below these commonly used floors it becomes difficult to meet vitamin, mineral and protein needs from food, and clinical guidelines reserve lower-calorie diets for medically supervised programs. Individual needs vary substantially, and a registered dietitian can personalize targets safely.
How to use this calorie calculator
- Select your sex and enter your age — both are inputs to the Mifflin-St Jeor equation.
- Enter your weight and height. Use the Metric/Imperial toggle to switch units.
- Choose the activity level that best matches a typical week, counting exercise and physically demanding work. When in doubt, pick the lower level — activity is commonly overestimated.
- Select a goal: maintain, mild loss (−250 kcal/day), standard loss (−500 kcal/day) or mild gain (+250 kcal/day).
- Read your daily calorie target alongside your maintenance calories (TDEE) and BMR. Weight-loss targets are automatically floored at 1200 kcal (women) or 1500 kcal (men).
The formula behind your calorie needs
The Mifflin-St Jeor equation predicts resting energy expenditure from weight, height, age and sex. Multiplying it by a standard activity factor — the widely used TDEE convention ranging from 1.2 for sedentary to 1.9 for extra active — estimates maintenance calories. Goal adjustments then subtract or add a fixed daily amount: 250 kcal/day for mild change and 500 kcal/day for standard weight loss, consistent with the gradual-change framing used by the CDC. Any weight-loss result that would fall below 1200 kcal/day (women) or 1500 kcal/day (men) is raised to that floor.
Common mistakes
- Overstating activity level — counting a desk job plus three gym sessions as "very active" inflates TDEE and stalls expected progress; most gym-going office workers fit "light" or "moderate".
- Eating at or below BMR in pursuit of faster results; targets below the 1200/1500 kcal floors make adequate nutrition difficult and belong only in medically supervised programs.
- Treating the estimate as exact — individual metabolism varies around the prediction, so adjust based on several weeks of real-world weight trend rather than a single number.
- Forgetting that calorie needs change with weight: after losing or gaining a meaningful amount, the target should be recalculated.
- Ignoring untracked calories from drinks, oils and snacks, which commonly explains a gap between an apparently correct target and no change on the scale.
Questions fréquentes
How many calories should I eat to lose weight?
A common evidence-aligned approach is to subtract 250 to 500 kcal per day from maintenance calories (TDEE), which corresponds to the gradual loss of roughly 0.5 to 1 kg (1–2 lb) per week described by the CDC as more sustainable than rapid loss. This calculator applies exactly that adjustment and never shows targets below 1200 kcal/day for women or 1500 kcal/day for men, floors below which unsupervised dieting risks inadequate nutrition.
What is the difference between BMR and maintenance calories?
Basal metabolic rate (BMR) is the energy the body uses at complete rest for breathing, circulation and cellular maintenance. Maintenance calories — total daily energy expenditure (TDEE) — add the energy spent on all movement and digestion, calculated here by multiplying BMR by an activity factor between 1.2 and 1.9. Eating at TDEE keeps weight roughly stable; BMR alone is not an eating target.
Why does this calculator use the Mifflin-St Jeor equation?
The Mifflin-St Jeor equation, published in 1990, was found to be the most accurate of the widely used resting-energy prediction equations for healthy adults in a systematic review by Frankenfield and colleagues for the American Dietetic Association (2005). It predicts resting energy expenditure within about 10% of measured values more often than the older Harris-Benedict equation, which it has largely replaced in dietetic practice.
Why won't the calculator show a target below 1200 or 1500 calories?
Below roughly 1200 kcal/day for women and 1500 kcal/day for men it becomes difficult to obtain adequate protein, vitamins and minerals from ordinary food. Clinical guidance, including the NIH/NHLBI obesity treatment guidelines, treats lower-calorie regimens as medically supervised interventions rather than self-directed diets. The calculator therefore raises any lower weight-loss result up to these floors.
How accurate are calorie calculators?
Prediction equations estimate the average for people of a given sex, age, height and weight. Individual resting metabolism typically falls within about 10% of the Mifflin-St Jeor prediction for most healthy adults, but larger deviations occur, and activity multipliers add further uncertainty. The practical approach is to start at the calculated target, track weight trend for two to four weeks, and adjust in small steps — or work with a registered dietitian.
Do calorie needs change with age?
Yes. In the Mifflin-St Jeor equation, predicted resting energy expenditure falls by about 5 kcal/day for each year of age, reflecting gradual changes in body composition and metabolism. Loss of muscle mass with age is a major driver, which is one reason resistance exercise and adequate protein are emphasized in healthy-aging guidance. Recalculate your needs periodically as age, weight and activity change.
How many calories do I need to gain weight?
A modest surplus of about 250 kcal/day above maintenance — the mild-gain option in this calculator — supports gradual weight gain of roughly 0.25 kg per week under the standard energy-balance approximation. Gradual surpluses combined with resistance training favor lean-mass gain over fat gain. People struggling to gain weight despite eating more should discuss it with a healthcare professional.
Références
- Mifflin MD, St Jeor ST, Hill LA, Scott BJ, Daugherty SA, Koh YO. A new predictive equation for resting energy expenditure in healthy individuals. American Journal of Clinical Nutrition 1990; 51(2): 241–247.
- Frankenfield D, Roth-Yousey L, Compher C. Comparison of predictive equations for resting metabolic rate in healthy nonobese and obese adults: a systematic review. Journal of the American Dietetic Association 2005; 105(5): 775–789.
- Centers for Disease Control and Prevention (CDC). Healthy Weight — Losing Weight: gradual weight loss of 1 to 2 pounds per week. cdc.gov.
- National Institutes of Health, National Heart, Lung, and Blood Institute. Clinical Guidelines on the Identification, Evaluation, and Treatment of Overweight and Obesity in Adults: The Evidence Report. NIH Publication No. 98-4083, 1998.
- Hall KD, Sacks G, Chandramohan D, et al. Quantification of the effect of energy imbalance on bodyweight. The Lancet 2011; 378(9793): 826–837.