Calorie Deficit Calculator
Pick a goal weight and a date. This tool works out the weekly rate the date demands, caps it at 1% of bodyweight per week, and tells you honestly when the date is asking for more than a safe rate can deliver.
Your numbers
The math, shown
The rate cap: evidence-based dieting guidance recommends losing 0.5–1% of bodyweight per week to protect muscle (Helms 2014). This tool never plans faster than 1% per week — if your date demands more, it tells you and shows the honest date instead.
The kcal-per-kg conversion: the classic static estimate is roughly 7,700 kcal per kg of weight lost (Wishnofsky 1958). Modern modelling shows the true figure varies between people and drifts as your body adapts (Hall 2008) — so treat the date as an estimate and re-run the numbers as your weight changes.
The floor: below roughly 1,200 kcal/day for women and 1,500 kcal/day for men — commonly used clinical minimums — it is hard to cover protein and micronutrient needs from food. Very low-calorie diets under 800 kcal/day are medical-supervision territory (NIDDK). If the target lands below the floor, the honest fix is a later date, not a bigger deficit.
These are population formulas — a starting point, not a prescription. Your training history, sleep, stress and cycle shift the real answer. That is what the 9-axis Body Scan measures.
Sources
- Helms ER, Aragon AA, Fitschen PJ. Evidence-based recommendations for natural bodybuilding contest preparation: nutrition and supplementation. J Int Soc Sports Nutr. 2014;11:20.
- Wishnofsky M. Caloric equivalents of gained or lost weight. Am J Clin Nutr. 1958;6(5):542–546.
- Hall KD. What is the required energy deficit per unit weight loss? Int J Obes (Lond). 2008;32(3):573–576.
- National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK). Very low-calorie diets require medical supervision. niddk.nih.gov — Health Information: Weight Management.
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These numbers are the first 10% of a plan.
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