What is a calorie deficit?
A calorie deficit means consuming fewer calories than your body burns each day. When you maintain a deficit, your body uses stored fat for energy, leading to weight loss. A deficit of 500 calories per day typically results in about 1 pound (0.5 kg) of weight loss per week.
BMR vs TDEE — what's the difference?
Your BMR (Basal Metabolic Rate) is the number of calories your body burns at complete rest to maintain basic life functions. Your TDEE (Total Daily Energy Expenditure) multiplies your BMR by an activity factor to account for daily movement and exercise. Your calorie target should be below your TDEE but above your BMR for healthy weight loss.
How large should my deficit be?
| Deficit / day | Weekly loss | Best for | Risk level |
|---|---|---|---|
| 250-300 kcal | ~0.5 lb | Lean individuals, long-term maintenance approach | Minimal |
| 500 kcal | ~1 lb | Most people — the evidence-based standard | Low |
| 750 kcal | ~1.5 lb | BMI 30+, shorter timelines | Moderate |
| 1,000+ kcal | ~2 lb | BMI 35+ with medical supervision only | High — muscle loss, fatigue |
Deficits larger than 1,000 calories per day can lead to muscle loss, fatigue, and nutrient deficiencies. Always consult a healthcare provider before starting a very low-calorie diet.
5 rules that make a deficit actually work
- Protein first. 0.7-1g per lb of goal body weight preserves muscle and controls hunger. See our protein intake calculator.
- Weigh weekly, not daily. Water retention hides fat loss for days — judge the 7-day average.
- Recalculate every 10-15 lbs. Your TDEE drops as you lose weight; a target that worked at 220 lbs stalls at 190.
- Don't eat back exercise calories. Trackers overestimate burn by 20-50%.
- Plan one maintenance week per 8-12 weeks. Diet breaks reduce adaptive hunger and improve adherence.
When diet alone isn't enough
For people with BMI 30+ (or 27+ with comorbidities), GLP-1 medications like semaglutide and tirzepatide produce 15-22% body weight loss in clinical trials — results diet alone rarely matches. They work partly by making a calorie deficit feel effortless. Check your GLP-1 eligibility or read our complete GLP-1 guide.
Frequently asked questions
How many calories should I eat to lose weight?
Eat 300-700 calories below your TDEE. A 500-calorie daily deficit produces about 1 pound of fat loss per week. Never eat below your BMR or under 1,200 calories (women) / 1,500 (men) without medical supervision.
Why am I not losing weight in a calorie deficit?
The usual culprits: underestimating portions (oils, drinks, weekends), overestimating activity, water retention masking fat loss, or metabolic adaptation. Track with a food scale for 2 weeks before lowering your target.
Is a 1,000-calorie deficit safe?
Only for people with BMI 35+ under medical supervision. For most people it causes muscle loss, fatigue, and rebound eating. Stick to 500-750 unless your doctor advises otherwise.
How accurate is this calculator?
Mifflin-St Jeor predicts BMR within ~10% for most adults — the best available without lab testing. Treat the result as a starting point, then adjust ±100-200 kcal based on 2-3 weeks of real-world progress.