Calorie Deficit Weight Loss Calculator
Find your daily calorie target to lose weight by a specific date. Enter your weight, goal, timeframe, activity level, age, gender, and height to get a personalized deficit.
Last updated: September 2026
Formula below · 3 sources (CDC, dietaryguidelines.gov, Wikipedia) · Updated Sep 2026
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About this calculator
This calculator combines the Mifflin-St Jeor BMR formula with your required calorie deficit to set a daily intake goal. BMR = (10 × kg) + (6.25 × cm) − (5 × age) + 5 for males, or − 161 for females, using your own height. That BMR is multiplied by an activity factor to get TDEE (Total Daily Energy Expenditure). A deficit is then subtracted: deficit per day = (weight-to-lose in lb × 3,500 kcal/lb) ÷ (weeks × 7). The result is your daily calorie target: TDEE − deficit. Since 1 lb of fat ≈ 3,500 kcal, losing 1 lb/week requires a 500 kcal/day deficit. Aggressive deficits beyond 1,000 kcal/day are generally not recommended without medical supervision.
How to use
Suppose a 35-year-old male, 70 in tall, weighing 200 lbs wants to reach 180 lbs in 10 weeks with a moderate activity level (factor 1.55). Step 1 — BMR: (10 × 90.7 kg) + (6.25 × 177.8 cm) − (5 × 35) + 5 = 907.2 + 1,111.3 − 175 + 5 ≈ 1,848 kcal. Step 2 — TDEE: 1,848 × 1.55 ≈ 2,865 kcal. Step 3 — daily deficit: (20 lbs × 3,500) ÷ (10 × 7) = 1,000 kcal/day. Step 4 — daily target: 2,865 − 1,000 ≈ 1,865 kcal/day. A 1,000 kcal/day deficit (2 lb/week) is the upper limit usually advised; a longer timeframe eases it.
Frequently asked questions
How large should a calorie deficit be for safe and sustainable weight loss?
Most health guidelines recommend a deficit of 500–1,000 kcal per day, which translates to roughly 0.5–1 lb of fat loss per week. Larger deficits can cause muscle loss, nutrient deficiencies, and metabolic adaptation. For most people, staying within this range produces steady results without compromising energy or health. Always consult a healthcare provider before pursuing an aggressive deficit.
What activity level multiplier should I use if I exercise three times a week?
Three workouts per week typically falls into the 'lightly active' category, which uses a multiplier of approximately 1.375 applied to your BMR. If those sessions are intense strength or cardio workouts, you may edge toward 'moderately active' at 1.55. Choosing too high a multiplier will overestimate TDEE and stall weight loss, so it's better to start conservative and adjust based on real-world results after two to four weeks.
Why does the calculator use the Mifflin-St Jeor formula instead of Harris-Benedict?
The Mifflin-St Jeor equation (1990) has been shown in peer-reviewed studies to predict resting metabolic rate within about 10% for most adults, outperforming the older Harris-Benedict equation (1919) in accuracy. Harris-Benedict tends to slightly overestimate calorie needs, which can slow progress. Mifflin-St Jeor is now the formula recommended by the Academy of Nutrition and Dietetics for clinical use. This calculator uses the Mifflin-St Jeor coefficients to give you the most reliable starting estimate.