🔥 Mifflin-St Jeor Formula · TDEE · Safe Deficit · Macro Planning · Goal Date
Calorie Deficit Calculator — How Many Calories to Lose Weight
Calculate your TDEE (Total Daily Energy Expenditure), daily calorie target for weight loss, macros (protein, carbs, fat), and exact goal date. Uses the Mifflin-St Jeor BMR formula — the most validated equation for most adults.
Primary fuel for exercise. Prioritize fiber-rich complex carbs for satiety and blood sugar stability.
Oats, sweet potato, brown rice, fruits, vegetables, legumes
Fats
20–30% of calories
9 kcal/g
Essential for hormones, fat-soluble vitamins (A,D,E,K), and satiety. Don't drop below 0.5 g/kg.
Olive oil, avocado, nuts, seeds, fatty fish, eggs
Calorie Deficit Calculator — How to Lose Weight With a Calorie Deficit
A calorie deficit is the foundation of all evidence-based weight loss — consuming fewer calories than your body burns (TDEE) forces the body to draw on stored fat for energy.
This calculator uses the Mifflin-St Jeor equation (1990), which has the highest validated accuracy for predicting Basal Metabolic Rate (BMR) in most adults, outperforming older equations like Harris-Benedict.
Your TDEE (Total Daily Energy Expenditure) = BMR × Activity Factor.
Your daily calorie target = TDEE − chosen deficit.
The Mifflin-St Jeor BMR Formula
Men: BMR = (10 × weight kg) + (6.25 × height cm) − (5 × age) + 5 Women: BMR = (10 × weight kg) + (6.25 × height cm) − (5 × age) − 161
This equation predicts resting metabolic rate to within ±10% for approximately 82% of the population.
It tends to overestimate BMR in obese individuals and underestimate in very muscular individuals.
For clinical accuracy in these populations, indirect calorimetry (metabolic cart testing) is the gold standard.
Why 500 kcal/Day Is the Standard Recommended Deficit
The 500 kcal/day deficit is the most commonly recommended starting point because:
(1) It produces approximately 0.5 kg/week (1 lb/week) of fat loss — a rate that preserves the majority of lean mass when combined with adequate protein;
(2) It is achievable through a combination of dietary reduction and moderate exercise;
(3) It is large enough to produce visible progress without triggering significant metabolic adaptation (the body lowering TDEE in response to sustained restriction);
(4) It allows for adequate nutrition without extreme restriction.
Deficits above 1,000 kcal/day are not recommended for most people because they significantly increase risk of lean mass loss, nutrient deficiencies, fatigue, and gallstone formation.
Why Protein Matters Most in a Calorie Deficit
During caloric restriction, the body can break down muscle tissue (lean mass) for energy alongside fat.
High protein intake (1.6–2.2 g/kg/day) is the most effective strategy to preserve lean mass while in a deficit.
Protein also has the highest thermic effect of food — approximately 20–30% of protein calories are burned in the process of digestion itself.
And protein is the most satiating macronutrient per calorie, reducing hunger and improving dietary adherence.
Always prioritize protein in a calorie deficit, even if it means reducing carbohydrates or fat to fit your calorie target.
Why isn't the scale moving even though I'm in a calorie deficit?
The scale can stall for several reasons despite a real calorie deficit: (1) Water retention — high sodium, carbohydrates, and hormonal fluctuations (especially in women) cause temporary water weight that masks fat loss. The scale may not move for 1–3 weeks then drop suddenly; (2) Digestive system contents — different foods, meal timing, and transit time cause 0.5–2 kg of variation; (3) TDEE overestimation — activity multipliers are estimates. If not losing after 3–4 weeks, reduce intake by 100–200 kcal/day; (4) Metabolic adaptation — sustained deficits reduce TDEE over time. Diet breaks (1–2 weeks at maintenance calories) can help reset before resuming. Track body measurements and how clothes fit — these often show progress when the scale does not.
What is the difference between BMR and TDEE?
BMR (Basal Metabolic Rate) is the number of calories your body burns at complete rest — just to maintain organ function, breathing, temperature regulation, and cellular repair. It represents approximately 60–70% of total daily energy expenditure. TDEE (Total Daily Energy Expenditure) is BMR multiplied by an activity factor to account for all movement throughout the day — exercise, non-exercise activity thermogenesis (NEAT — fidgeting, walking, standing), and the thermic effect of food. Your weight loss calorie target is set below your TDEE, not your BMR. Eating at your BMR level while active means you are already in a significant deficit.
Should I eat back calories burned during exercise?
Whether to eat back exercise calories depends on how your TDEE was calculated. This calculator uses an activity multiplier that incorporates your regular exercise — so exercise calories are already factored into your TDEE, and eating them back would cancel your deficit. If you use the "Sedentary" multiplier and add exercise on top, you may want to eat back 50–75% of exercise calories to avoid too large a total deficit. The most practical approach: pick the activity level that best matches your typical week, set your deficit, and eat consistently regardless of day-to-day exercise variation. Avoid the trap of "earning" food through exercise, which often leads to overestimating burn and underestimating intake.
How many calories is too low for safe weight loss?
General safe minimums: Women should not go below 1,200 kcal/day; Men should not go below 1,500 kcal/day. These represent minimums for meeting basic micronutrient needs. Below these levels, vitamin and mineral deficiencies become difficult to avoid even with supplements, and muscle loss accelerates significantly. Very Low Calorie Diets (VLCD) of 800 kcal/day or less are a medical intervention used only under physician supervision for severe obesity (BMI >30) with significant comorbidities. They require medical monitoring, meal replacements, and typically produce 1.5–2.5 kg/week loss. The maximum recommended sustainable deficit for most people is 1,000 kcal/day, producing approximately 1 kg (2.2 lbs) per week.