How the calculation works
First we estimate your BMR (basal metabolic rate) — the calories your body burns at complete rest — using the Mifflin-St Jeor equation, which studies show is the most accurate general-purpose formula:
Women: BMR = 10×kg + 6.25×cm − 5×age − 161
Multiplying BMR by an activity factor (1.2 for sedentary up to 1.9 for very active) gives your TDEE — total daily energy expenditure, i.e. your maintenance calories. Eating below TDEE loses weight; above it gains.
Picking a sensible deficit
Half a kilogram (about one pound) of body fat stores roughly 3,500 kcal, so a 500 kcal daily deficit loses about 0.5 kg per week. Larger deficits work short-term but raise the odds of muscle loss, fatigue, and rebound. Most guidelines advise not dropping below ~1,500 kcal/day for men and ~1,200 kcal/day for women without medical supervision — this calculator floors its targets at 1,000 kcal as a hard safety limit.
Tips for using your number
- Treat it as a starting point. Formulas carry ±10% error. Track your weight for 2–3 weeks; if it isn't moving as expected, adjust by 150–200 kcal.
- Recalculate as you go. Every 5 kg of change shifts your TDEE by roughly 70–100 kcal.
- Protein protects muscle in a deficit — around 1.6–2.2 g per kg of body weight is a common evidence-based range for active people.
This tool provides general estimates for educational purposes and is not medical advice. Consult a healthcare professional for guidance specific to you.
Frequently asked questions
How many calories should I eat to lose weight?
Subtract 250–500 kcal from your maintenance (TDEE) for a loss of 0.25–0.5 kg per week. A 70 kg moderately active 30-year-old man with a TDEE of ~2,570 kcal would target roughly 2,070 kcal for steady loss.
What is TDEE?
Total daily energy expenditure — everything you burn in a day: your resting metabolism (BMR), digestion, daily movement, and exercise. It's your break-even calorie intake; weight change comes from eating consistently above or below it.
Why am I not losing weight in a calorie deficit?
Usually the deficit isn't real: food logging commonly under-counts by 20–40%, restaurant portions surprise, and weekends erase weekday deficits. Water retention can also mask fat loss for weeks. Measure honestly for 2–3 weeks before concluding the math is wrong.
Should I eat back exercise calories?
If you selected an activity level that already includes your workouts, no — they're counted. Only add calories for genuinely unusual extra activity, and even then fitness trackers overestimate burn by 20–90%, so add conservatively.
How accurate are calorie calculators?
Within about ±10% for most people, which is 150–250 kcal either way. Genetics, muscle mass, and hormone status shift real needs. Use the estimate as a baseline, then calibrate against your actual weight trend.