Transparent by design — computed in your browser from a published formula, not a black box. Verified 2026-05-25. Based on: Wishnofsky (1958) ↗ · Hall energy-deficit model (2008) ↗ Full methodology →
NUTRITION · DEFICIT PLANNING
Calorie Deficit Calculator
Estimate the daily calorie deficit you need to reach a target bodyweight in a given number of weeks.
Result
Projected Weight Path
Linear projection at the computed weekly rate.
How to use it
- Run the TDEE Calculator first to establish your maintenance calories, then enter that number here along with your weight-loss goal and timeline.
- A 500-calorie daily deficit theoretically produces 1 lb/week loss (3,500 cal = 1 lb fat). In practice expect 0.6–0.8 lb/week average due to water fluctuation and metabolic adaptation.
- Cap your deficit at 25% of TDEE to preserve lean mass. For a 2,200 TDEE, max sustainable deficit is 550 calories/day. Exceeding this accelerates muscle protein breakdown.
- If the scale stalls for 3+ weeks, do NOT simply cut more calories — first recalculate TDEE at your current (lower) body weight. A 10 lb loss typically lowers TDEE by 50–100 calories.
- Plan diet breaks: 1–2 weeks at maintenance calories every 6–8 weeks during a sustained cut partially reverses metabolic adaptation and significantly improves long-term adherence.
Questions people usually ask
How large a deficit should I use to lose fat without losing muscle?
Research supports 300-500 calories below TDEE for most people. This yields 0.5-1 lb weekly loss. Deficits exceeding 25% of TDEE accelerate muscle protein breakdown — a 150 lb person should not exceed ~500-600 calorie daily deficit. Protein intake of 0.8-1g per lb of body weight is the most important muscle-preservation factor.
Why did I stop losing weight on the same deficit?
Three reasons: (1) Adaptive thermogenesis — metabolism slows by 5-15% during sustained restriction. (2) Weight loss itself reduces TDEE — lighter bodies burn fewer calories. (3) Food tracking drift — portion accuracy decreases over time. Recalculate your deficit based on current weight and consider a 1-2 week diet break at maintenance.
Is it safe to eat 1200 calories a day?
1200 calories is a minimum threshold commonly cited, but adequacy depends on body size. A 130 lb, 5 foot 4 inch lightly active woman might have a TDEE around 1700 calories — a 500 calorie deficit brings her to 1200, which is adequate. A larger person eating 1200 calories would be in an extreme deficit (40%+) risking muscle loss, fatigue, and nutrient deficiencies.
Formula
See the math
The underlying formula with variables defined, derivation shown, and a worked example with units.
For agents
Use in an agent
Same math, same result shape as the UI above — as a static ES module. No HTTP request, no auth, no rate limit.
import { compute } from "https://aifithub.io/engines/calorie-deficit-calculator.js";Contract: /contracts/calorie-deficit-calculator.json Types: /engines/calorie-deficit-calculator.d.ts Full agent guide →
Related Resources
Learn the decision before you act
Every link here is tied directly to Calorie Deficit Calculator. Use the explanation, formula, examples, and benchmarks to pressure-test the calculator output from first principles.
How To Use
5 STEPSHow to Use Body Recomposition Planner
Plan your body recomposition with our calculator. Learn how to strategically lose fat while building muscle with personalized calorie and macro targets.
ReadGuide
7 MIN READHow to Break a Calorie Deficit Plateau (5 Fixes)
How to break a calorie deficit Plateau (5 Fixes): weight loss stalled? Before cutting more calories, check these 5 common causes: tracking errors, metabolic a.
ReadComparison
9 CRITERIACalorie Counting vs Intuitive Eating Diet for Weight Loss
Calorie counting vs intuitive eating diet: counting gives faster fat loss, intuitive eating protects maintenance. See who each fits and how to combine both.
ReadFormula
5 VARIABLESBMR Formula (Mifflin-St Jeor)
BMR = 10·mass_kg + 6.25·height_cm − 5·age + sex_constant. Mifflin-St Jeor 1990. Sex constant: +5 male, −161 female. Used as the baseline for TDEE and deficit math.
ReadExamples
4 EXAMPLESBmr Examples
Explore diverse BMR examples to understand your baseline metabolism for effective fat loss. Learn how age, weight, and lifestyle impact your daily calorie.
ReadChecklist
11 ITEMSTDEE Tracking Checklist: Your First 30 Days
A week-by-week checklist for calibrating your TDEE estimate with real-world data. Covers measurement, tracking, and adjustment over 4 weeks.
ReadRelated deep dive
All articles →Read further
Long-form context behind the calculator output.
- Pillar·10 min
Body Composition: The Four Lenses
Body composition through four lenses: BMI, FFMI, measured body fat, and energy balance. What each metric answers, where it fails, and the deep dives.
Read - Pillar·13 min
Body Recomposition for Lifters: The Calorie Math
Body recomposition is real for specific populations under specific conditions. The four conditions, protein math scaled to LBM, 12-week example.
Read - Article·8 min
How to Break a Weight-Loss Plateau
Breaking a weight-loss plateau: adaptive thermogenesis math, refeed protocols, training-volume changes, and the four leverage points before changing tools.
Read
Continue With Related Tools
Plan a realistic body-recomp timeline with body-fat targets, training frequency, calorie pacing, and protein guidance.
Open →TDEE calculator: estimate your total daily energy expenditure using the Mifflin-St Jeor equation and activity multipliers.
Open →Macro calculator: convert your calorie target into daily protein, carbs, and fat grams based on your goal and split preference.
Open →One-rep max calculator: estimate your 1RM using Epley, Brzycki, and Lombardi formulas with a practical percentage table.
Open →