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.
- Keep the pace to about 0.5-1% of body weight a week (Helms 2014): elite athletes losing 1.4% a week gained no lean mass, while those losing 0.7% a week did (Garthe 2011).
- 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.
- Consider diet breaks: in the MATADOR trial, men who alternated 2 weeks of dieting with 2 weeks at maintenance lost more fat than those who dieted continuously (Byrne 2018).
Questions people usually ask
How large a deficit should I use to lose fat without losing muscle?
For lean lifters dieting for a physique goal, Helms et al. 2014 recommend losing 0.5-1% of body weight a week, with protein at 2.3-3.1 g/kg of fat-free mass, to retain muscle. For a 70 kg lifter that is 0.35-0.7 kg a week, roughly a 400-770 kcal daily deficit at first (at about 7,700 kcal per kg of fat). Because the rule is a share of body weight, it scales the deficit to your size.
Why did I stop losing weight on the same deficit?
Three reasons: (1) a lighter body burns fewer calories, so the same intake is a smaller deficit; (2) energy use also falls further than the weight loss alone predicts, by about 100 kcal a day of resting expenditure in one controlled study (Müller 2015); (3) food tracking drifts as portions creep up. Recalculate your deficit at your current weight and consider a 1-2 week 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.
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Background on the Calorie Deficit Calculator
- Guide How to Break a Calorie Deficit Plateau (5 Fixes)
To break a calorie deficit plateau, check five causes before cutting calories: tracking errors, a lower TDEE, water shifts, less movement and short sleep.
- 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.
- Checklist Weight Loss Checklist
A weight loss checklist: a 300-500 kcal deficit, about 0.5-1% of body weight a week, protein at each meal, strength work and steps, sleep and weekly reviews.
- Statistics Calorie Deficit Statistics: Fat Loss by the Numbers
Calorie deficit statistics: average loss rates, adherence, metabolic adaptation and long-term maintenance, each figure with the study it comes from.
- Statistics Intermittent Fasting Statistics: Outcomes & Effects
Intermittent fasting statistics: weight loss, metabolic effects, adherence and head-to-head trials against daily calorie restriction, each with a source.
- Statistics Weight Loss Statistics: Real-World Outcomes by the Numbers
Weight loss statistics: how many people keep weight off, real-world deficit outcomes, predictors of success and treatment results, each with a source.
Articles
- 8 min read Mifflin, Harris-Benedict, Cunningham: Resting Metabolism Methodology
Mifflin, Harris-Benedict, and Cunningham RMR equations: how each was derived, who the calibration cohort was, and the 5% Harris-Benedict overestimate.
- 7 min read Best Free TDEE & Calorie Calculators 2026: Honest vs the Apps
Best free TDEE and calorie calculators 2026: free Mifflin-St Jeor tools beat app upsells. How they work and an honest take vs MyFitnessPal.
- 7 min read Is Apple Watch Calorie Count Accurate? (2026 Evidence)
Is the Apple Watch calorie count accurate in 2026? The best wrist estimator in named research, but still off ~27%; read it as a trend, not truth.
By goal
Use it from an agent or code
Any agent can run this calculator by URL: put the inputs in the query string and get JSON back, with the inputs that used defaults and a line to cite (add format=md for markdown). MCP clients reach it through https://aifithub.io/mcp.
In code, import the same module; it runs where you import it, with no request or key.
import { compute } from "https://aifithub.io/engines/calorie-deficit-calculator.js";Input and output contract, TypeScript types and the guide for agents.