Nutrition
Calorie Deficit Calculator
Estimate the daily calorie deficit you need to reach a target bodyweight in a given number of weeks.
Result
Your maintenance falls as the weight comes off, so this intake loses less each week. Recalculate your TDEE every four weeks or so and adjust the target.
Projected weight path
An even weekly rate, the planning line; real loss slows as maintenance falls.
Formula from Wishnofsky (1958) and Hall energy-deficit model (2008), checked against the source on May 25, 2026.
What does the Calorie Deficit Calculator calculate, and which formula does it use?
The Calorie Deficit Calculator works out the daily deficit needed to reach a goal weight over your chosen timeline, using the energy-balance rule that one kilogram of body weight is about 7,700 kcal. It divides that total across the weeks, subtracts it from your TDEE for a daily calorie target, and flags the pace as aggressive when the deficit exceeds 25% of TDEE or drops intake below 1,200 kcal.
Last updated .
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.
The formula, worked through
- Formula Calorie Deficit Formula
The calorie deficit formula: daily deficit = TDEE minus intake, with 1 lb fat about 3,500 cal and 1 kg about 7,700 cal, plus a worked weekly-loss example.
- Formula Intermittent Fasting Window Formula
Intermittent fasting window formula: eating window = first meal time + 4-10 hours by protocol, meals spaced evenly across it; 5:2 sets two low days at a quarter of usual intake.
- Formula Body Recomposition Formula
Body recomposition formula: target_weight = LBM / (1 − target_BF%/100). weekly_fat_loss = (current_weight − target_weight) / weeks.
Related calculators
- Planning Body Recomposition Planner
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- Nutrition TDEE Calculator
Estimate your daily energy expenditure with Mifflin-St Jeor + activity factors.
- Nutrition Macro Calculator
Convert calorie targets into protein, carbs, and fat grams for your goal.
- Strength One-Rep Max Calculator
Estimate one-rep max with Epley, Brzycki, and Lombardi formulas.
Background on the Calorie Deficit Calculator
- Guide How 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.
- Comparison Calorie 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.
- Examples Calorie Deficit Examples
Explore practical calorie deficit examples tailored for diverse lifestyles, from sedentary office workers to active individuals, for sustainable fat loss.
- Checklist Cutting Phase Checklist
Run a structured cutting phase with this actionable checklist. Learn to set calorie deficits, optimize macros, adjust training, and track progress.
- Statistics Calorie Deficit Statistics: Fat Loss by the Numbers
Key statistics on calorie deficits, weight loss rates, adherence, metabolic adaptation, and long-term maintenance. Evidence from meta-analyses.
- Learn What Is Calorie Deficit? Simply Explained
What is calorie deficit: understand effective weight loss with our clear explanation of 'Calorie Deficit'.
Articles
- 10 min read 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.
- 13 min read 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.
- 8 min read 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.
By goal
Use it from code
The same calculation as a JavaScript module you can import. It runs where you import it, with no request, key or rate limit.
import { compute } from "https://aifithub.io/engines/calorie-deficit-calculator.js";Input and output contract, TypeScript types and the guide for agents.