Planning
As of 2026-04-24
How Calorie Deficit Calculator works
Methodology for the Calorie Deficit Calculator: formulas, coefficients, data sources, assumptions, and known limitations.
Scope
Calculates the daily calorie deficit required to hit a target bodyweight by a target date, using the 3500 kcal/lb rule of thumb.
Formula
required_daily_deficit = (target_fat_loss_kg * 7700) / days. Target calories = TDEE - required_daily_deficit.
Coefficients
| Parameter | Value | Note |
|---|---|---|
| Energy per kg fat | ~7700 kcal | |
| Safe weekly loss | 0.5–1.0% bodyweight |
Data sources
- Wishnofsky M. Caloric equivalents of gained or lost weight. Am J Clin Nutr. 1958;6(5):542-546. — PMID 13594881. Origin of the 3500 kcal/lb (~7700 kcal/kg) heuristic.
- Hall KD. What is the required energy deficit per unit weight loss? Int J Obes (Lond). 2008;32(3):573-576. — PMID 17848938. Quantifies why the 3500 rule over-predicts long-run loss.
- Thomas DM, Martin CK, Heymsfield S, et al. A simple model predicting individual weight change in humans. J Biol Dyn. 2011;5(6):579-599. — PMID 24522441. Dynamic weight-loss model that refines Wishnofsky's static rule.
- Helms ER, Zinn C, Rowlands DS, Brown SR. A systematic review of dietary protein during caloric restriction in resistance trained lean athletes. Int J Sport Nutr Exerc Metab. 2014;24(2):127-138. — PMID 24092765. Supports the 'weight lost is primarily fat' assumption when protein and resistance training are adequate.
Assumptions
- Weight lost is primarily fat (high-protein + resistance training reinforces this).
- TDEE input is current, not pre-diet.
Approximation range
The 7700 kcal/kg rule over-predicts long-run fat loss by 10–30% because metabolic adaptation drops TDEE over a multi-month cut.
For cuts longer than ~12 weeks, use the tool's output as a starting deficit and recalibrate monthly from the scale trend.
Limitations
- Doesn't model water, glycogen, or bowel-content fluctuations that dominate week-1 scale readings.
- Very aggressive targets (>1% BW/week) are flagged but not blocked.
Reproducibility
Goal -5 kg in 12 weeks (84 days). Required = 5*7700/84 = 458 kcal/day deficit. With TDEE 2800, daily target 2342 kcal.
Change log
- 2026-04-24: methodology page first published.
Related tools
- Body Recomposition Planner — Plan body-fat reduction pace, deficit targets, and protein needs around a timeline.
- Hybrid Training Planner — Build a weekly schedule that balances running and lifting with interference warnings and recovery guidance.