How the Weight Loss Calorie Calculator Works
The calculator first estimates your Basal Metabolic Rate (BMR) using the Mifflin-St Jeor equation, which is considered the most accurate BMR formula for the general population. It then multiplies your BMR by an activity factor reflecting your exercise habits and daily movement level. The result is your Total Daily Energy Expenditure (TDEE) — the number of calories you burn in a typical day.
To lose weight, you need to eat below your TDEE. A deficit of 500 calories per day produces approximately one pound of fat loss per week, since one pound of body fat contains roughly 3,500 calories. A deficit of 750 calories per day accelerates this to about 1.5 pounds per week. The calculator recommends a moderate deficit that balances speed of results with sustainability and nutritional adequacy.
The calculator also sets a floor of 1,200 calories per day for women and 1,500 for men to ensure you meet minimum nutritional needs. Eating below these thresholds for extended periods risks nutrient deficiencies, muscle loss, and metabolic slowdown that can make long-term weight management harder. If your calculated deficit falls below these levels, the tool recommends increasing activity rather than further reducing food intake.
Example: Calculating a Weight Loss Calorie Target
A 35-year-old woman, 5 feet 6 inches tall, weighing 170 pounds, who exercises 3 times per week.
- BMR calculated using Mifflin-St Jeor: approximately 1,490 calories per day.
- TDEE with moderate activity factor (1.55): 1,490 x 1.55 = approximately 2,310 calories per day.
- For 1 pound per week loss, subtract 500: target intake is 1,810 calories per day.
- For 1.5 pounds per week, subtract 750: target is 1,560 calories per day (still above the 1,200 floor).
- At 1,810 calories daily, she can expect to reach her goal weight in a healthy, sustainable timeframe.
Tips for Accurate Results
- Aim to lose no more than 1-2 pounds per week for sustainable results. Faster weight loss increases the risk of muscle loss, nutritional deficiency, and eventual rebound weight gain.
- Track your food intake for at least one week using an app to understand your current eating patterns before making drastic changes to your calorie target.
- Prioritize protein intake at 0.7-1.0 grams per pound of body weight during a caloric deficit to preserve lean muscle mass while losing body fat.
- Recalculate your calorie needs after every 10-15 pounds lost, because your TDEE decreases as your body weight decreases.
Frequently Asked Questions
How many calories should I eat to lose weight?
The answer is individual and depends on your current TDEE. Most people can lose weight safely by eating 500 calories below their TDEE, which produces about 1 pound of fat loss per week. For a sedentary woman with a TDEE of 1,800, that means eating around 1,300 calories. For an active man with a TDEE of 2,800, the target would be approximately 2,300 calories. Never go below 1,200 calories for women or 1,500 for men without medical supervision.
Is a 1,200-calorie diet safe?
A 1,200-calorie diet is generally considered the minimum safe intake for women under medical guidance. It can be appropriate for small-framed, sedentary women seeking modest weight loss. For most people, 1,200 calories is too restrictive to meet nutritional needs long-term. It often leads to fatigue, nutrient deficiencies, and metabolic adaptation that stalls weight loss and promotes regain.
Why does weight loss slow down over time?
As you lose weight, your body requires fewer calories to maintain its smaller size. Your BMR decreases and you burn fewer calories during activity because you are moving less mass. This means the same calorie intake that initially created a deficit may eventually become closer to your new maintenance level. Recalculating your TDEE and adjusting intake or increasing activity restarts progress.
Should I eat back calories burned during exercise?
Partially. Exercise calorie estimates from fitness trackers are often inflated by 20-50%. Eating back all reported exercise calories can eliminate your deficit entirely. A safer approach is to eat back only 50% of estimated exercise calories, or to use a TDEE calculation that already factors in your exercise frequency rather than adding exercise calories separately.