Estimate days needed to reach a goal weight at a given deficit. This dedicated page is built for fast, clean calculations and search visibility.
Enter your values, click calculate, and see the result instantly. The page uses a simple, focused layout to improve usability on mobile and desktop.
How to use this calculator
- Open the calorie deficit calculator page.
- Enter the required values in the form fields.
- Click Calculate to see the result and breakdown.
- Use the related links to explore similar tools.
How a calorie deficit produces fat loss
Body fat is stored energy. One kilogram of fat contains approximately 7,700 calories. To lose 1 kg of fat, you need a cumulative calorie deficit of 7,700 kcal — achievable over roughly 2 weeks at a 500 kcal/day deficit. A 500 kcal/day deficit (roughly 10–20% below TDEE) is considered the sweet spot — large enough for meaningful weekly loss (approximately 0.4–0.5 kg/week) while small enough to preserve muscle mass and energy levels.
Larger deficits (1,000 kcal/day) accelerate fat loss but significantly increase muscle loss and metabolic slowdown.
Why aggressive deficits backfire
- Metabolic adaptation: The body reduces TDEE by 15–20% under prolonged severe restriction (adaptive thermogenesis). A 1,200 kcal diet maintained for months produces far less fat loss than predicted.
- Muscle loss: Below 1,200 kcal (women) or 1,500 kcal (men), protein intake is often inadequate and muscle tissue is catabolised for fuel.
- Rebound eating: Severe restriction increases hunger hormones (ghrelin), making the deficit unsustainable and leading to overeating cycles.
Target 0.5–1% of body weight loss per week. Track food for 2 weeks to establish your real baseline TDEE, then reduce by 400–500 kcal. Keep protein high (1.6–2g/kg) to preserve muscle. Expect a plateau every 4–6 weeks as TDEE adjusts — this is normal, not failure.