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Calorie Deficit Calculator

A calorie deficit is the foundation of weight loss — you need to consume fewer calories than your body burns. This calculator estimates your Total Daily Energy Expenditure (TDEE), then subtracts your chosen deficit to give you a daily calorie target. It also projects how quickly you can expect to lose weight and warns you if your intake drops too low.

Reviewed by GetHealthyCalculators Editorial Team · Updated April 14, 2026

Quick Answer

A moderate deficit of 500 calories per day leads to roughly 1 lb (0.45 kg) of weight loss per week. Your TDEE minus your deficit equals your daily calorie target.

These results are estimates based on general formulas and are not a substitute for professional medical advice. Consult a healthcare provider before making health decisions.

Enter your details above to calculate your calorie deficit.

How the Formula Works

  1. Calculate your TDEE using the Mifflin-St Jeor equation and an activity multiplier.

    TDEE = BMR × Activity Multiplier

  2. Choose a deficit level or enter a custom deficit amount.

    Mild = 250 cal/day | Moderate = 500 cal/day | Aggressive = 750 cal/day | Extreme = 1,000 cal/day

  3. Subtract the deficit from your TDEE to get your daily calorie target.

    Daily Calories = TDEE − Deficit

  4. Estimate weekly weight loss using the 3,500-calorie rule.

    Weekly Loss (lbs) = (Deficit × 7) / 3,500

  5. If you entered a goal weight, divide total weight to lose by weekly loss rate to estimate time to goal.

Methodology & Sources

Reviewed and updated April 14, 2026 · Prepared by GetHealthyCalculators Editorial Team

This calculator pairs the Mifflin-St Jeor BMR equation (Am J Clin Nutr 1990) with standard activity multipliers to estimate TDEE, then applies a linear deficit model based on the classic Wishnofsky 3,500-kcal-per-pound approximation (Wishnofsky, Am J Clin Nutr 1958). Kevin Hall and colleagues (Lancet 2011) have shown that real-world weight loss is non-linear and that the 3,500-kcal rule systematically over-predicts long-term loss as metabolism adapts. Treat projections as upper-bound estimates and consult a registered dietitian or physician before adopting deficits larger than 500 kcal/day, especially if pregnant, breastfeeding, managing a chronic condition, or recovering from disordered eating.

References

  • A new predictive equation for resting energy expenditure in healthy individuals (Mifflin MD et al., Am J Clin Nutr 1990;51:241–247) · American Journal of Clinical Nutrition
  • Caloric equivalents of gained or lost weight (Wishnofsky M., Am J Clin Nutr 1958;6:542–546) · American Journal of Clinical Nutrition
  • Quantification of the effect of energy imbalance on bodyweight (Hall KD et al., Lancet 2011;378:826–837) · The Lancet
  • Long-term persistence of hormonal adaptations to weight loss (Sumithran P et al., N Engl J Med 2011;365:1597–1604) · New England Journal of Medicine
  • Persistent metabolic adaptation 6 years after "The Biggest Loser" competition (Fothergill E et al., Obesity 2016;24:1612–1619) · Obesity (Silver Spring)
  • 2020–2025 Dietary Guidelines for Americans · U.S. Department of Health and Human Services & USDA
  • AACE/ACE Comprehensive Clinical Practice Guidelines for Medical Care of Patients with Obesity · American Association of Clinical Endocrinologists

Limitations

  • The 3,500-calorie-per-pound rule (Wishnofsky 1958) is a simplification — Hall et al. (Lancet 2011) demonstrated that actual weight loss is non-linear as metabolism adapts.
  • TDEE estimates have a margin of error of roughly 10%, so your actual calorie needs may differ.
  • This calculator does not account for adaptive thermogenesis, body composition shifts, or hormonal changes (leptin, ghrelin, thyroid) that blunt weight loss over months.
  • Extreme deficits can lead to muscle loss, nutrient deficiencies, gallstones, fatigue, menstrual disruption, and metabolic slowdown.
  • Very-low-calorie diets (below 1,200 kcal/day for women, 1,500 kcal/day for men) should only be undertaken with medical supervision.
  • This tool is informational and not a substitute for advice from a registered dietitian or physician, especially for adolescents, pregnant or breastfeeding people, older adults, and anyone with metabolic or eating-disorder history.

Frequently Asked Questions

What is a calorie deficit?
A calorie deficit means you consume fewer calories than your body burns (your TDEE). This forces your body to use stored energy — primarily body fat — to make up the difference, leading to weight loss over time.
How big of a calorie deficit is safe?
Most health professionals recommend a deficit of 500 calories per day (about 1 lb loss per week) as a sustainable target. Deficits larger than 1,000 calories per day are generally not recommended without medical supervision.
Will a calorie deficit cause muscle loss?
Some muscle loss is common during a deficit, but you can minimize it by eating adequate protein (0.7–1 g per pound of body weight), performing resistance training, and keeping your deficit moderate rather than extreme.
Why is there a minimum calorie warning?
Eating below 1,200 calories (women) or 1,500 calories (men) per day can make it very difficult to meet essential nutrient needs and may slow your metabolism. If your deficit brings you below this threshold, the calculator warns you to consult a healthcare provider.
How accurate is the time-to-goal estimate?
The time-to-goal projection assumes a constant rate of weight loss, which rarely happens in practice. Metabolic adaptation, water weight fluctuations, and lifestyle changes all affect the timeline. Use it as a rough guide, not an exact schedule.
Should I eat back exercise calories?
Your TDEE already factors in your typical activity level. If you do additional exercise beyond your selected activity level, you may want to eat back some of those calories, but most people overestimate calories burned during exercise. A conservative approach is to eat back roughly half.
What is metabolic adaptation and how does it affect a deficit?
Metabolic adaptation (adaptive thermogenesis) is the body's tendency to reduce resting energy expenditure beyond what weight loss alone predicts. Sumithran et al. (NEJM 2011) and Fothergill et al. (Obesity 2016) documented hormonal and metabolic changes that persist for years after significant loss, which is why plateaus and regain are common.
How often should I recalculate my calorie target?
Recalculate every 5–10 lbs (2.5–5 kg) of weight change, or every 4–6 weeks. As weight drops your BMR drops too, so the same calorie target becomes a smaller deficit over time.
When should I stop a deficit?
Pause a deficit if you experience persistent fatigue, dizziness, menstrual irregularity, loss of libido, poor sleep, mood changes, or loss of gym performance. These can signal under-eating relative to your needs and warrant a diet break and clinician check-in.

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