Calorie Deficit Calculator
Plan your weight loss with a safe daily calorie deficit and see your week-by-week projection
Your Weight Loss Plan
Understanding Calorie Deficits for Weight Loss
A calorie deficit occurs when you consume fewer calories than your body burns in a day. Your Total Daily Energy Expenditure (TDEE) represents the total number of calories your body uses for basal metabolism, physical activity, the thermic effect of food, and non-exercise movement. When you eat below your TDEE, your body must draw on stored energy -- primarily body fat -- to make up the difference. This fundamental energy balance principle is the foundation of all evidence-based weight loss approaches. One pound (0.45 kg) of body fat contains approximately 3,500 calories of stored energy, which means a daily deficit of 500 calories translates to roughly one pound of fat loss per week.
The size of your calorie deficit directly determines how fast you lose weight, but bigger is not always better. A moderate deficit of 300 to 500 calories per day is generally considered the sweet spot for sustainable fat loss, allowing you to preserve lean muscle mass, maintain energy levels, and avoid the hormonal disruptions that come with severe restriction. Research published in the International Journal of Obesity found that aggressive deficits exceeding 1,000 calories per day can trigger metabolic adaptation, where your body downregulates its metabolic rate to conserve energy, making continued weight loss progressively harder and increasing the risk of regaining weight once the diet ends.
Your timeline for weight loss should balance ambition with physiological safety. Most nutrition and obesity medicine guidelines recommend losing no more than 0.5 to 1 kilogram (1 to 2 pounds) per week. Faster rates of loss are sometimes appropriate for individuals with a very high body mass index under medical supervision, but for most people, a steady rate within this range preserves muscle, supports immune function, and is far more likely to produce lasting results. This calculator helps you find the deficit needed for your specific timeline while flagging any plan that exceeds safe limits.
Keep in mind that weight loss is rarely perfectly linear. Water retention, hormonal fluctuations, stress, sleep quality, and changes in physical activity can all cause day-to-day and week-to-week scale weight to fluctuate by 1 to 3 kilograms even when fat loss is proceeding on track. Focus on the overall trend rather than any single weigh-in. If you are tracking your progress and find that your actual results diverge significantly from the projection, recalculate your TDEE (which decreases as you lose weight) and adjust your intake accordingly. Recalculating every 4 to 6 weeks helps keep your plan aligned with your changing metabolism.
How to Use This Calculator
- Select your preferred unit system (Metric or Imperial) using the toggle at the top of the form. All weight fields will update accordingly.
- Enter your current body weight. For best accuracy, weigh yourself first thing in the morning before eating or drinking.
- Enter your target weight -- the weight you want to reach. Make sure this is a realistic and healthy goal for your height and body frame.
- Enter your TDEE (Total Daily Energy Expenditure) in calories. If you do not know your TDEE, use our TDEE Calculator to find it first.
- Enter your desired timeline in weeks. This is how long you want to take to reach your target weight.
- Click "Calculate Deficit" to see your required daily deficit, target intake, weekly loss rate, a severity meter, a week-by-week weight projection chart, and safety warnings if your plan is too aggressive.
Frequently Asked Questions
What is a safe calorie deficit for weight loss?
Most health organizations and registered dietitians recommend a deficit of 500 to 750 calories per day for safe, sustainable weight loss. This produces a loss rate of roughly 0.5 to 0.75 kg (1 to 1.5 lbs) per week. Deficits above 1,000 calories per day are generally considered aggressive and increase the risk of muscle loss, nutrient deficiencies, hormonal disruption, and metabolic slowdown. Very low calorie diets (below 1,200 kcal/day for women or 1,500 kcal/day for men) should only be followed under medical supervision.
How do I know my TDEE to use in this calculator?
Your TDEE (Total Daily Energy Expenditure) is the total number of calories your body burns each day including your basal metabolic rate, physical activity, and the thermic effect of food. You can estimate it using our TDEE Calculator, which applies the Mifflin-St Jeor equation and an activity multiplier. For a more precise estimate, track your calorie intake and body weight for 2 to 3 weeks: if your weight stays stable, your average daily intake equals your TDEE. Fitness trackers and smart watches also provide rough TDEE estimates based on heart rate data.
Why does the calculator show a safety warning?
The safety warning appears when your required calorie deficit exceeds 1,000 kcal per day or when your resulting daily intake would drop below recommended minimums (1,200 kcal for women, 1,500 kcal for men). Deficits this large are associated with significant muscle loss, reduced bone density, impaired immune function, gallstone formation, and a dramatic slowing of metabolism. When a warning appears, the calculator also shows a recommended safe timeline that keeps your deficit at a sustainable level.
Will I lose muscle along with fat during a calorie deficit?
Some muscle loss is almost inevitable during any calorie deficit, but you can minimize it substantially. Research consistently shows that consuming adequate protein (1.6 to 2.2 grams per kilogram of body weight per day), engaging in resistance training at least 2 to 3 times per week, getting sufficient sleep (7 to 9 hours), and keeping your deficit moderate (no more than 500 to 750 kcal/day) together preserve the vast majority of lean muscle mass during fat loss. Crash diets with extreme deficits cause the most muscle loss.
Why has my weight loss stalled even though I am in a deficit?
Weight loss plateaus are extremely common and have several causes. First, as you lose weight your TDEE decreases because your smaller body requires fewer calories, so a deficit that worked initially may no longer be sufficient. Second, metabolic adaptation can reduce your metabolic rate by 5 to 15 percent beyond what weight loss alone would predict. Third, water retention from stress, sodium intake, menstrual cycles, or new exercise routines can temporarily mask fat loss on the scale. Recalculate your TDEE at your new weight and adjust your intake, or consider a brief diet break to reset metabolic hormones.
How often should I recalculate my calorie deficit?
You should recalculate your deficit every 4 to 6 weeks, or after every 3 to 5 kg (7 to 11 lbs) of weight loss, whichever comes first. As your body weight decreases, your basal metabolic rate drops and you burn fewer calories during physical activity (since you are moving less mass). If you do not adjust your intake downward, your deficit shrinks over time and weight loss slows or stops. Recalculating keeps your plan aligned with your current metabolism.
Is it better to create a deficit through diet or exercise?
Both work for creating an energy deficit, but a combination is most effective and sustainable. Dietary changes tend to be more efficient for creating large deficits because it is far easier to skip a 500-calorie dessert than to burn 500 calories through exercise (which requires roughly 45 to 60 minutes of vigorous activity). However, exercise contributes to muscle preservation, cardiovascular health, and improved mood. Most experts recommend creating 70 to 80 percent of your deficit through diet and 20 to 30 percent through increased physical activity.
