Caloric Deficit Calculator — Lose Weight Safely
Calculate the daily calorie deficit you need to reach your goal weight by a target date. Based on TDEE and BMR. Shows safe deficit ranges, recommended macro splits, estimated weekly loss, and how long to reach your goal at different deficit levels.
Quick Presets
Step 1 — Personal Stats
Step 2 — Your Goal
What Is the Caloric Deficit Calculator — Lose Weight Safely?
This calculator uses the Mifflin-St Jeor equation — the most validated BMR formula for healthy adults — to compute your maintenance calories (TDEE) and then works out exactly how big a daily deficit or surplus you need to reach your goal weight by your target date.
- ›BMR (Mifflin-St Jeor) — accounts for your weight, height, age, and sex. The most accurate of the common BMR equations for the general population.
- ›TDEE with five activity levels — multiplies BMR by a factor from 1.2 (desk job, no exercise) up to 1.9 (physical job and twice-daily training).
- ›Safety assessment — automatically flags your deficit as Safe (<750 kcal/day), Aggressive (750–1000), or Unsafe (>1000) and warns when you fall below the clinical minimum (1,200 kcal for women, 1,500 for men).
- ›Macro splits — converts your daily calorie target into three practical macro distributions: balanced, high-protein, and low-carb.
- ›Weekly projection table — shows your expected weight every week until goal, up to 52 weeks.
- ›Scenario comparison — shows how a conservative 250 kcal deficit and an aggressive 750 kcal deficit compare to your plan.
Formula
BMR — Mifflin-St Jeor Formula
Men: BMR = 10 × weight(kg) + 6.25 × height(cm) − 5 × age + 5
Women: BMR = 10 × weight(kg) + 6.25 × height(cm) − 5 × age − 161
TDEE — Total Daily Energy Expenditure
TDEE = BMR × Activity Factor
Sedentary: ×1.2 · Light: ×1.375 · Moderate: ×1.55 · Very active: ×1.725 · Extra: ×1.9
Caloric Deficit Formula
Daily calories to eat = TDEE − deficit
Weekly weight loss (kg) = (deficit × 7) / 7700
Note: 1 kg of body fat ≈ 7,700 kcal
| Symbol | Name | Description |
|---|---|---|
| BMR | Basal Metabolic Rate | Calories burned at complete rest — the minimum your body needs to sustain life |
| TDEE | Total Daily Energy Expenditure | BMR adjusted for activity level — your actual daily calorie burn |
| deficit | Caloric deficit | The daily shortfall between TDEE and calories consumed |
| 7700 | kcal per kg of fat | Approximate energy stored per kilogram of body fat (widely used estimate) |
| AF | Activity Factor | A multiplier (1.2–1.9) that accounts for how active you are each day |
How to Use
- 1Enter personal stats: Fill in your age, sex, height, and current weight. Switch the unit toggle for cm/ft or kg/lbs.
- 2Choose activity level: Select the option that best matches your typical week, from sedentary (desk job) to extra active (physical job or twice-daily training).
- 3Select your approach: Choose "Lose weight" for a deficit, "Maintain" to see your TDEE, or "Gain weight" for a caloric surplus.
- 4Enter your goal weight: Type in your target weight. The unit follows whatever you chose for current weight.
- 5Set your timeline: Either type how many weeks you want to reach your goal, or pick a specific target date using the date picker.
- 6Press Calculate: Results appear instantly: BMR, TDEE, daily calorie target, deficit, weekly loss rate, safety badge, macro splits, and comparison scenarios.
- 7Check the projection table: Expand the weekly projection to see your expected weight every week until your goal date.
Example Calculation
30-year-old male, 85 kg, 180 cm, moderately active — goal: 75 kg in 20 weeks
Step 1: Calculate BMR (Mifflin-St Jeor, male)
BMR = 10 × 85 + 6.25 × 180 − 5 × 30 + 5
= 850 + 1125 − 150 + 5
BMR = 1,830 kcal/day
Step 2: Apply activity factor (moderate = ×1.55)
TDEE = 1,830 × 1.55
TDEE = 2,837 kcal/day
Step 3: Required deficit for 10 kg loss in 20 weeks
Total kcal needed = 10 kg × 7,700 = 77,000 kcal
Days available = 20 × 7 = 140 days
Daily deficit = 77,000 / 140
Deficit = 550 kcal/day → eat 2,287 kcal/day
Results for this example
| Week | Projected weight (kg) | Deficit/day (kcal) |
|---|---|---|
| 1 | 84.5 | 550 |
| 4 | 83.0 | 550 |
| 8 | 81.0 | 550 |
| 12 | 79.0 | 550 |
| 16 | 77.0 | 550 |
| 20 ★ | 75.0 | 550 |
Understanding Caloric Deficit — Lose Weight Safely
What Is a Caloric Deficit?
A caloric deficit occurs when you consistently consume fewer calories than your body burns. Your body then turns to stored fat (and, to a lesser degree, muscle) for the energy shortfall. Over time, this produces measurable weight loss. The magnitude of the deficit determines both the speed of loss and the safety of the process.
- ›One pound of fat ≈ 3,500 kcal. One kilogram of fat ≈ 7,700 kcal.
- ›A 500 kcal/day deficit produces roughly 0.5 kg (1 lb) of loss per week.
- ›The same math works in reverse for a surplus — eating more than TDEE leads to weight gain.
- ›Important caveat: as you lose weight, your TDEE also decreases because you are carrying less mass. Real-world loss is therefore slightly slower than the simple math predicts after the first few weeks.
How TDEE and BMR Are Calculated
Your Basal Metabolic Rate (BMR) is the number of calories your body burns at complete rest — just to keep your heart beating, lungs breathing, and cells functioning. The Mifflin-St Jeor equation is the most widely cited and validated formula for estimating BMR in healthy adults:
- ›Men: BMR = 10 × weight(kg) + 6.25 × height(cm) − 5 × age + 5
- ›Women: BMR = 10 × weight(kg) + 6.25 × height(cm) − 5 × age − 161
Your TDEE multiplies BMR by an activity factor that accounts for the energy burned through movement. Sedentary people (×1.2) burn little beyond their BMR, while those with physical jobs or twice-daily training (×1.9) nearly double it.
Why Mifflin-St Jeor?
A 2005 meta-analysis in the Journal of the American Dietetic Association tested four common BMR equations against indirect calorimetry measurements. The Mifflin-St Jeor equation was the most accurate for a diverse population, with approximately 70% of predictions falling within 10% of measured BMR. The Harris-Benedict equation (published 1919) is still commonly cited but consistently overestimates BMR in modern sedentary populations.
How Big Should Your Caloric Deficit Be?
The appropriate deficit depends on your starting point, goal, and timeline. As a general framework:
- ›250 kcal/day (conservative) — approximately 0.25 kg/week loss. Ideal for those close to goal weight or those who want to minimize muscle loss.
- ›500 kcal/day (moderate) — approximately 0.5 kg/week. The most commonly recommended deficit, balancing pace with sustainability.
- ›750 kcal/day (aggressive) — approximately 0.75 kg/week. Acceptable for those with a significant amount to lose but requires careful nutrient management.
- ›>1,000 kcal/day (not recommended) — increases risk of muscle wasting, nutrient deficiencies, metabolic adaptation, and hair loss.
Why You Should Not Cut Calories Too Aggressively
Very low-calorie diets produce rapid initial weight loss, but much of this comes from glycogen (and associated water), not fat. Several physiological consequences make extreme deficits counterproductive in the medium term:
- ›Metabolic adaptation. The body reduces non-essential energy expenditure (NEAT — non-exercise activity thermogenesis) in response to prolonged restriction, reducing TDEE by 10–15%.
- ›Muscle catabolism. Without adequate protein and a moderate deficit, the body breaks down muscle tissue for energy.
- ›Nutrient deficiencies. Eating below 1,200–1,500 kcal/day makes it extremely difficult to meet micronutrient needs without supplementation.
- ›Hormonal disruption. Leptin (the satiety hormone) falls, ghrelin (the hunger hormone) rises, making adherence progressively harder.
The Role of Macros in a Deficit
Within a caloric deficit, the composition of your diet matters as much as the total. Three practical macro strategies are shown in this calculator:
| Strategy | Protein % | Carbs % | Fat % | Best for |
|---|---|---|---|---|
| Balanced | 30% | 35% | 35% | General fat loss with muscle retention |
| High protein | 40% | 30% | 30% | Athletes, gym-goers, preserving lean mass |
| Low carb | 35% | 20% | 45% | Reducing insulin spikes, keto-adjacent |
Protein is especially important in a deficit. At 0.8–1.0 g per pound of body weight (1.8–2.2 g/kg), dietary protein provides the amino acids needed to preserve muscle tissue and keeps satiety high, making adherence easier.
Frequently Asked Questions
What is the difference between BMR and TDEE?
BMR is the number of calories your body burns at complete rest — no movement, no digestion, just staying alive.
TDEE scales BMR by your activity level:
- ›Sedentary (desk job, no exercise): TDEE = BMR × 1.2
- ›Lightly active (exercise 1–3×/week): TDEE = BMR × 1.375
- ›Moderately active (exercise 3–5×/week): TDEE = BMR × 1.55
- ›Very active (hard exercise 6–7×/week): TDEE = BMR × 1.725
- ›Extra active (physical job or 2× daily training): TDEE = BMR × 1.9
TDEE is the number to use as your baseline. Eating at TDEE = maintenance; eating below TDEE = deficit (weight loss); eating above TDEE = surplus (weight gain).
How many calories should I cut to lose 1 pound per week?
The math for a 1 lb/week loss:
- ›1 lb of fat ≈ 3,500 kcal
- ›Weekly deficit needed = 3,500 kcal
- ›Daily deficit = 3,500 / 7 = 500 kcal/day
For metric users: 1 kg ≈ 7,700 kcal → a 1,100 kcal/day deficit would lose 1 kg/week (which is likely too aggressive — aim for 0.5 kg/week at most).
In practice, the first week may show more loss due to glycogen depletion and water loss. Weeks 2–4 typically show the true underlying fat loss rate.
Is a 1,000 calorie deficit safe?
A 1,000 kcal/day deficit is at the edge of what clinical guidelines consider safe:
- ›Risk of muscle loss increases significantly above 750 kcal/day deficit
- ›Nutrient deficiencies become likely below 1,200 kcal (women) / 1,500 kcal (men)
- ›Metabolic adaptation (body reducing TDEE) accelerates at extreme deficits
- ›Medical supervision is recommended for Very Low Calorie Diets (VLCD, <800 kcal/day)
For most people, a 500–750 kcal/day deficit achieves meaningful results while preserving muscle and remaining nutritionally adequate.
Why is the Mifflin-St Jeor equation used instead of Harris-Benedict?
Both equations estimate BMR, but Mifflin-St Jeor is more accurate for most people today:
- ›Harris-Benedict was derived from a small sample in 1919 — lifestyle has changed significantly
- ›Mifflin-St Jeor was validated in a larger, more representative 1990 study
- ›Harris-Benedict overestimates BMR by 5–15% on average in sedentary modern adults
- ›Mifflin-St Jeor predicts within 10% of indirect calorimetry for ~70% of subjects
Other equations like Katch-McArdle (requires body fat %) can be more precise if you know your lean body mass, but Mifflin-St Jeor is the best general-purpose formula for total body weight inputs.
How much protein should I eat in a caloric deficit?
Protein targets during a deficit (per kg of current body weight):
- ›General fat loss: 1.6–2.0 g/kg (0.7–0.9 g/lb)
- ›Resistance training + fat loss: 1.8–2.4 g/kg (0.8–1.1 g/lb)
- ›Athletes in aggressive deficit: up to 2.4–3.1 g/kg in some studies
Protein has a thermic effect of about 25–30% (compared to ~5–10% for carbs and ~0–3% for fat), meaning it costs more energy to digest and metabolise — further supporting its role in a deficit.
What happens when weight loss slows down or stalls?
Plateaus happen for predictable physiological reasons:
- ›Your TDEE drops as you lose weight — so the same food intake no longer creates a deficit
- ›Metabolic adaptation: NEAT decreases by 10–15% in response to caloric restriction
- ›Leptin levels fall, reducing the satiety signal and increasing hunger
- ›Glycogen and water fluctuations can mask real fat loss for weeks
Practical solutions: recalculate your calorie targets at your new weight every 4–5 kg lost, incorporate a 1–2 week maintenance break to restore metabolic rate, and ensure sleep and stress are managed (cortisol promotes fat retention).
Can I lose weight without counting calories?
Calorie counting is one of many approaches. Effective implicit deficit strategies include:
- ›Prioritising high-protein, high-volume foods that are filling but lower in calories (vegetables, lean meats, legumes)
- ›Reducing ultra-processed foods which are engineered to be hyperpalatable and easy to overeat
- ›Eating slowly and recognising fullness cues — it takes ~20 min for satiety signals to register
- ›Cutting liquid calories (alcohol, sodas, juices) which add energy without satiety
- ›Intermittent fasting as a time-based restriction strategy
That said, understanding your personal TDEE and calorie targets — even if you only track occasionally — helps you build intuition about food choices and portions.
Does the calculator save my inputs between sessions?
All inputs are persisted to your browser's localStorage:
- ›Age, sex, height, weight, and activity level are saved automatically
- ›Goal weight, timeline, and approach are also preserved
- ›Data stays entirely in your browser — nothing is sent to any server
- ›Inputs are restored the next time you visit the page
Click Reset All to clear both the form and the saved localStorage entry.