How Deficitly calculates your calories

Reviewed 1 November 2026

Deficitly builds your daily burn from parts you can check, instead of multiplying by a vague activity level. All of it runs in your browser; nothing you enter is sent anywhere.

1. Resting burn (BMR)

The Mifflin-St Jeor equation: 10 × weight (kg) + 6.25 × height (cm) − 5 × age, plus 5 for men or minus 161 for women. If you enter a body-fat percentage, Deficitly uses Katch-McArdle instead: 370 + 21.6 × lean mass (kg). See resting burn by age and weight.

2. Daily life

Standing, chores and fidgeting outside of counted steps: 10% of BMR.

3. Steps

Steps become distance using your stride (41.5% of height for men, 41.3% for women), and distance becomes calories at 0.5 kcal per kg of body weight per km, the cost of walking above resting. Steps taken during counted workouts (walks, runs, sports) are taken out so they aren't counted twice. See what 10,000 steps burn.

4. Workouts

Each activity has a MET value from the 2024 Adult Compendium of Physical Activities. A session adds (MET − 1) × weight (kg) × hours: the "− 1" removes the resting calories already counted in BMR. Weekly sessions are averaged per day. Padel has no Compendium entry yet; it uses casual paddleball (6 METs).

5. Digestion

Digesting food costs about 10% of what you eat; at maintenance that's 10% of the total.

6. The range

Equations miss individuals by about ±10%, so the result comes with a range. Deficitly errs a little low for very active people on purpose. Your weight trend over 3–4 weeks is the final word.

7. Losing or gaining weight

About 7,700 calories per kg of body fat (the classic 3,500 per pound). The default pace is 0.5% of body weight a week, with at most 1% for loss and 0.5% for gain. Plans never go below 1,200 calories a day for women or 1,500 for men, and there are no loss plans for people under 18 or with a BMI under 18.5. You can plan by pace, by a date, or start from what you eat now. See how many calories to eat to lose weight.

8. Protein, carbs and fat

Protein 1.8 g per kg of a reference weight while losing (1.6 when maintaining). The reference is lean mass scaled to a healthy body-fat level if you know your body fat, otherwise the lowest of your weight, your target and the weight for a BMI of 25. Fat is 30% of calories for women and 25% for men, never under 0.8 g/kg (women) or 0.6 g/kg (men). Carbs get the rest. See how much protein to lose weight.

Sources

• Mifflin MD, St Jeor ST, Hill LA, et al. A new predictive equation for resting energy expenditure in healthy individuals. Am J Clin Nutr 1990;51(2):241–247.
• McArdle WD, Katch FI, Katch VL. Exercise Physiology: Nutrition, Energy, and Human Performance (Katch-McArdle equation).
• Herrmann SD, Willis EA, Ainsworth BE, et al. 2024 Adult Compendium of Physical Activities: A third update of the energy costs of human activities. Journal of Sport and Health Science, 2024;13(1):6-12. doi:10.1016/j.jshs.2023.10.010
• Jäger R, Kerksick CM, Campbell BI, et al. International Society of Sports Nutrition position stand: protein and exercise. J Int Soc Sports Nutr 2017;14:20.
• 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.
• U.S. Department of Agriculture and U.S. Department of Health and Human Services. Dietary Guidelines for Americans, 2020–2025 (fibre: 14 g per 1,000 calories).

Limits

Deficitly gives estimates for healthy adults. It isn't medical advice and isn't meant for pregnancy, breastfeeding, eating disorders or medical conditions that affect weight. Questions about your health belong with a doctor or registered dietitian.