Maximum Fat Loss Calculator

Inputs

Units:
Metric (cm, kg)
Gender
Years
cm
kg
%
Must stay below current
Moderate · 3-4 workouts/week · x1.55
85% of max

100% uses the full deficit from the 31 kcal/lb fat-mass rule. Lower percentages scale it down (e.g. 70% = 0.7 × max deficit).

Notes: We apply the 31 kcal per lb of fat-mass rule (Alpert, 2005). Estimates are bounded by a minimum intake floor.

Results

Maintenance (TDEE)

2664 kcal

Max daily deficit

1164 kcal 1.06 kg/week max

Chosen deficit

989 kcal 85% of max

Target calorie intake

1675 kcal/day
Intake floor: 1500 kcal

Expected weekly loss

0.90 kg (1.98 lb)

Loss rate

1.2%/week
Aggressive

Fat mass

18.7 kg (41.3 lb)

Lean body mass

59.3 kg (130.7 lb)

Protein target

119 g/day
~474 kcal

Goal weight

72.3 kg (159.4 lb)
Assuming lean mass stays constant

Fat to lose

5.7 kg (12.6 lb)

Timeline preview

Projected time to goal: 6 weeks (~1.5 months)

Timeline assumes adherence to the chosen deficit and steady lean mass.
Educational use only. Consult a qualified professional before attempting aggressive weight loss protocols.

Sources

  • Alpert SS. A limit on the energy transfer rate from the human fat store in hypophagia. J Theor Biol. 2005;233(1):1–13. PMID 15615615 · doi:10.1016/j.jtbi.2004.08.029 — fat-mobilization energy-transfer limit (≈31 kcal/lb/day).
  • Mifflin MD, St Jeor ST, et al. A new predictive equation for resting energy expenditure in healthy individuals. Am J Clin Nutr. 1990;51(2):241–247. PMID 2305711 — basis for the TDEE estimate.
  • Wishnofsky M. Caloric equivalents of gained or lost weight. Am J Clin Nutr. 1958;6(5):542–546. PMID 13594881 — ≈3,500 kcal/lb (7,700 kcal/kg) used for weekly weight-change estimates.
  • Hall KD. Body fat and fat-free mass inter-relationships: Forbes's theory revisited. Br J Nutr. 2007;97(6):1059–1063. PMID 17367567 · doi:10.1017/S0007114507691946 — further reading on how body composition changes with energy deficit.

This calculator estimates how large a daily calorie deficit could theoretically be supported by your fat stores, based on the amount of energy that body fat can release per day. The underlying idea is that fat tissue has a limited rate at which it can supply energy; the more fat mass a person carries, the higher this theoretical ceiling, and the leaner they are, the lower it becomes.

To produce its estimates, the tool combines three established calculations: maintenance energy expenditure (TDEE) from the Mifflin-St Jeor equation, fat mass derived from body weight and body-fat percentage, and a maximum fat-mobilization rate of roughly 31 kcal per pound of fat mass per day reported by Alpert. Weekly weight-change estimates use the conventional energy value of about 7,700 kcal per kilogram (≈3,500 kcal per pound) of body weight.

How it works (formula)

The calculation steps are as follows:

  • Fat mass (lb) = body weight × (body-fat % ÷ 100)
  • Lean body mass = body weight − fat mass
  • Maintenance (TDEE) = Mifflin-St Jeor BMR × activity factor
  • Maximum daily deficit (kcal) = min( 31 × fat mass in lb, an upper cap, and TDEE − intake floor )
  • Weekly change = (daily deficit × 7) ÷ 7,700 kcal/kg
  • Goal weight = lean body mass ÷ (1 − goal body-fat % ÷ 100), assuming lean mass stays constant

The figure of about 31 kcal per pound of fat per day corresponds to the energy-transfer limit of roughly 290 kJ/kg/day described by Alpert (2005). As body-fat percentage falls, fat mass decreases and this theoretical ceiling drops, which is reflected in the calculator's output.

These figures are population-level estimates for general informational and educational purposes and will not reflect any individual's actual metabolism or body composition.