What is a calorie deficit?
A calorie deficit is the gap between the calories you eat and the calories your body burns. Burn more than you consume and your body covers the difference by tapping stored energy — mostly body fat — which is exactly how weight loss happens. Every successful diet, whatever its name, works by creating this deficit.
The starting point is your maintenance calories, also called your TDEE (Total Daily Energy Expenditure). Subtract a daily deficit from that number and you have your weight-loss target. This calculator estimates your TDEE from the Mifflin-St Jeor equation and your activity level, then applies the deficit you choose.
How big a deficit is safe?
A safe, sustainable rate of loss is about 0.5–1% of your bodyweight per week. For most people that lands between a 250 and 750 calorie daily deficit:
- Mild (−250/day) — about 0.25 kg (0.5 lb) per week; easiest to stick to and best for preserving muscle.
- Moderate (−500/day) — about 0.5 kg (1 lb) per week; the popular middle ground.
- Aggressive (−750/day) — about 0.75 kg (1.5 lb) per week; faster, but harder to sustain and hungrier.
Whatever pace you pick, this calculator holds a 1,200-calorie floor. Eating below that for any length of time risks muscle loss, low energy, and nutrient gaps — and it usually backfires through rebound eating.
Why the scale isn’t linear
Fat loss is steady; the number on the scale is not. Day to day your weight swings with water retention, salt, carbs, hormones, and the food still in your gut — easily a kilo or two in either direction. That is why a perfect deficit can show a flat or even rising scale for a week.
Plateaus are also normal: as you get lighter, your TDEE drops, so the same intake becomes a smaller deficit over time. Weigh yourself the same way a few mornings a week, track the multi-week trend rather than single readings, and re-run this calculator as your weight changes.
Hitting the target every day
Knowing your number is easy; staying under it daily is the hard part. Swoodie calculates the same target from your profile and then does the daily work: scan a plate or a barcode to log calories instantly, generate recipes that fit your remaining budget, and follow your weight-loss plan without guesswork. You can also check your BMI or fine-tune your maintenance number with the TDEE calculator.
Frequently asked questions
What is a calorie deficit?
A calorie deficit means eating fewer calories than your body burns in a day (your TDEE). When you do this consistently, your body makes up the shortfall by using stored energy — mostly body fat — so you lose weight. It is the only mechanism behind every diet that works.
How many calories should I eat to lose weight?
Subtract your chosen deficit from your maintenance calories (TDEE). A 500-calorie daily deficit loses roughly 0.5 kg (1 lb) per week and is the most popular sustainable pace. This calculator never recommends below 1,200 calories per day for safety.
Is a 1,000-calorie deficit safe?
A very large deficit can work short term but raises the risk of muscle loss, fatigue, nutrient gaps, and rebound eating. Most experts cap weekly loss at about 0.5–1% of your bodyweight. A 250–500 calorie deficit is more sustainable for the long run.
Why am I not losing weight in a deficit?
The most common reasons are underestimating portions, untracked extras (drinks, oils, bites), water-weight fluctuations masking real fat loss on the scale, or a TDEE estimate that is slightly high. Track consistently for 2–3 weeks and judge the trend, not a single day.
How long will it take to reach my goal weight?
Divide the weight you want to lose by your weekly loss rate. For example, losing 10 kg at 0.5 kg per week takes about 20 weeks. Real progress is rarely perfectly linear, so treat the estimate as a guide and re-check it as your weight changes.
This tool provides general estimates for healthy adults and is not medical advice. For therapeutic diets, eating disorders, or medical conditions, consult a registered dietitian or doctor before changing your calorie intake.