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Learn more →Calorie Deficit Calculator — TDEE & Weight Loss
Enter your age, sex, height, weight, activity level, and weekly loss goal. The calculator uses the Mifflin-St Jeor formula to compute your BMR and TDEE, then subtracts a safe daily deficit to give you a target calorie intake. A minimum floor of 1,500 kcal for men and 1,200 kcal for women is enforced.
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Enter your details to calculate your calorie deficit.
How it works
What is a calorie deficit — and how TDEE and BMR fit in
Your basal metabolic rate (BMR) is the number of calories your body needs just to stay alive at rest — breathing, circulating blood, regulating temperature. This calculator uses the Mifflin-St Jeor equation, which is consistently more accurate than the older Harris-Benedict formula in large validation studies. For men: BMR = 10 × weight(kg) + 6.25 × height(cm) − 5 × age + 5. For women the constant is −161 instead of +5, reflecting typical differences in lean mass.
Total daily energy expenditure (TDEE) multiplies BMR by an activity factor: 1.2 for largely sedentary people up to 1.9 for those doing twice-daily training or physical labor. TDEE is your maintenance level — the number of calories at which your weight is stable. A calorie deficit means eating below your TDEE. When the deficit is sustained, your body draws on stored fat (and to a lesser degree, glycogen and lean tissue) to make up the shortfall, producing weight loss over time.
Safe deficit rates and the 3,500 kcal rule
The widely cited rule is that 1 lb of body fat stores roughly 3,500 kcal of energy, and 1 kg stores about 7,700 kcal. So a daily deficit of 500 kcal should produce ~0.5 kg (1 lb) of weight loss per week. In practice, weight loss is not perfectly linear — water retention, muscle changes, and metabolic adaptation all play a role — but the estimate is reliable enough for planning.
Most guidelines treat 0.5–1.0 kg per week as the safe zone. Faster rates increase muscle loss and can trigger metabolic slowdown (sometimes called 'adaptive thermogenesis'), where the body reduces expenditure in response to a sustained large deficit. Very-low-calorie diets below 800 kcal/day should only be done under medical supervision. This calculator enforces a floor of 1,500 kcal for men and 1,200 kcal for women — if your chosen goal pushes below that floor, the floor value is used and a warning is shown.
Diet vs. exercise vs. combination — what the evidence shows
Diet changes are more effective than exercise alone for creating a calorie deficit, simply because it is easier to cut 500 kcal from food than to burn 500 kcal through activity (a 70 kg person running at moderate pace for about 45 minutes). However, exercise provides independent benefits — improved insulin sensitivity, preserved muscle mass during a cut, cardiovascular health, and mental well-being — that diet alone does not.
The most successful long-term fat-loss approaches combine a moderate dietary deficit with regular resistance training and cardio. Resistance training during a deficit is especially valuable: it signals the body to preserve lean muscle, so a greater proportion of lost weight comes from fat. Aim for at least two sessions per week targeting major muscle groups. For the dietary side, prioritizing protein (1.6–2.2 g/kg of body weight) and high-volume, low-calorie foods like vegetables makes hitting a deficit easier without constant hunger.
Frequently asked questions
›How accurate is the Mifflin-St Jeor formula?
It is consistently ranked as the most accurate of the commonly used BMR prediction equations for non-obese adults, with a mean error of roughly 5–10% in validation studies. It is less reliable at the extremes — very high body fat, extreme muscularity, or unusual metabolic conditions. For most people it is the best practical starting point.
›Why does the calculator have a minimum calorie floor?
Eating below 1,200 kcal/day (women) or 1,500 kcal/day (men) makes it very difficult to meet basic micronutrient needs without supplementation, and increases risk of muscle loss, gallstones, and metabolic adaptation. These floors reflect broadly accepted clinical guidelines. If your goal requires going below them, a smaller weekly loss target or professional guidance is recommended.
›My actual weight loss is slower than the calculator predicts. Why?
Several factors can cause this: overestimation of activity level, underestimation of calories consumed, metabolic adaptation after weeks of deficit, water retention masking fat loss, or measurement errors. Weigh yourself under consistent conditions (same time of day, same clothing) and track a weekly average rather than daily readings.
›Should I eat back calories burned during exercise?
It depends on how you selected your activity level. If you chose 'moderately active' or higher to reflect your exercise, your TDEE already includes those calories — do not eat them back. If you chose 'sedentary' to keep things conservative and track workouts separately, eating back a portion (50–75%) of estimated exercise calories is reasonable.
›Is 1.0 kg per week too aggressive?
For most people, 1.0 kg/week requires roughly a 1,100 kcal/day deficit, which is substantial. It is feasible for heavier individuals where the absolute deficit represents a smaller percentage of TDEE, but for lighter individuals it often pushes below safe minimums. A rate of 0.5 kg/week is generally a better starting point — it is sustainable, minimizes muscle loss, and is far more likely to be maintained long-term.
›How do I account for muscle gain while losing fat (body recomposition)?
This calculator targets weight loss, not body recomposition. Recomp — losing fat while gaining muscle simultaneously — is possible but slower, typically requires eating at or near maintenance with high protein and consistent resistance training. A dedicated TDEE calculator at maintenance calories paired with progressive lifting is the better tool for that goal.
›What happens to my TDEE as I lose weight?
TDEE decreases as you lose weight, because a lighter body requires fewer calories to maintain. This is why weight loss plateaus occur. Re-run this calculator every 4–6 weeks with your updated weight to recalibrate. Alternatively, use a slightly more aggressive deficit from the start knowing you will need to adjust.
›Does this data get sent anywhere?
No. All calculations happen entirely in your browser. No personal data leaves your device.
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