Calorie Deficit Calculator
Calculate your daily calorie target for weight loss based on TDEE, desired weekly loss rate, and activity level with projected timeline to goal weight.
What This Calculator Does
This calorie deficit calculator estimates your Basal Metabolic Rate (BMR) using the Mifflin-St Jeor equation, calculates your Total Daily Energy Expenditure (TDEE) based on activity level, and determines the daily calorie target needed to achieve your desired weekly weight loss rate. It also projects the timeline to reach your goal weight and flags targets that fall below medically recommended minimums.
The Formula
The Mifflin-St Jeor equation (1990, validated in 2005) is considered the most accurate BMR prediction equation for most adults. TDEE multiplies BMR by an activity factor ranging from 1.2 (sedentary) to 1.9 (extremely active). The calorie deficit is based on the energy content of body fat: approximately 7,700 calories per kilogram (3,500 per pound). A 500-calorie daily deficit produces roughly 0.45 kg (1 lb) of weekly weight loss.
Step-by-Step Example
Enter your stats
Male, 30 years old, 180 lbs (81.6 kg), 70 inches (178 cm), moderately active.
Calculate BMR and TDEE
BMR: 10(81.6) + 6.25(178) - 5(30) + 5 = 1,782 cal. TDEE: 1,782 x 1.55 = 2,762 cal/day.
Set deficit
Target 1 lb/week loss. Daily deficit: 500 cal. Target intake: 2,762 - 500 = 2,262 cal/day.
Project timeline
Goal weight: 160 lbs. Total loss: 20 lbs. At 1 lb/week: approximately 20 weeks to goal.
Real-World Use Cases
Weight Loss Planning
Calculate a sustainable calorie target that produces steady fat loss without extreme restriction.
Rate Comparison
Compare how different weekly loss rates (0.5, 1.0, 1.5, 2.0 lbs/week) affect your daily calorie target and timeline.
Maintenance Transition
Once you reach your goal weight, use your TDEE as your maintenance calorie target to prevent regain.
Common Mistakes to Avoid
Setting too aggressive a deficit. Losing more than 1% of body weight per week increases muscle loss, metabolic adaptation, and the likelihood of regaining weight.
Not adjusting as you lose weight. Your BMR and TDEE decrease as you get lighter. Recalculate every 10 to 15 pounds lost to maintain your target deficit.
Ignoring the minimum safe intake. Women should not consume below 1,200 calories/day and men should not go below 1,500 calories/day without medical supervision.
Relying solely on calorie counting without considering food quality. A 2,000-calorie diet of whole foods supports better satiety, energy, and health markers than 2,000 calories of processed foods.
Frequently Asked Questions
Accuracy and Disclaimer
This calculator uses the Mifflin-St Jeor equation and provides estimates for informational purposes only. It is not a substitute for professional medical or dietary advice. Individual metabolic rates vary based on genetics, body composition, hormones, medications, and health conditions. Consult a physician or registered dietitian before beginning any weight loss program, especially if you have diabetes, heart disease, eating disorders, thyroid conditions, or other medical conditions. Never consume below 1,200 calories/day (women) or 1,500 calories/day (men) without medical supervision. Rapid weight loss can cause serious health complications.
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