If you want to lose fat, you need a consistent calorie deficit. This Calorie Deficit Calculator estimates your daily calorie target from your body weight, activity level, and your chosen deficit size so you can plan meals and track progress.
Use it to choose a deficit that matches your goal, then adjust based on real-world results over 2–4 weeks.
What Is a Calorie Deficit?
A calorie deficit happens when you eat fewer calories than your body uses. Your body then makes up the difference by using stored energy (mostly body fat, but also some glycogen and sometimes lean tissue).
The size of the deficit and how long it lasts determine how much weight you can expect to lose.
Key Terms (Simple Definitions)
- Maintenance calories: Calories your body burns in a typical day at your current activity level.
- Calorie deficit: The number of calories below maintenance you plan to eat each day.
- Daily calorie target: Maintenance minus deficit. This is your target intake for the day.
- Estimated weight change: A rough expectation based on energy balance.
How This Calculator Works
This calculator computes daily maintenance calories using the Mifflin–St Jeor equation, then subtracts your chosen deficit to estimate your daily calorie target.
It also estimates weekly weight change using the common conversion that 3,500 calories ≈ 1 lb of body fat (and 7,700 calories ≈ 1 kg).
Step 1: Estimate BMR (Basal Metabolic Rate)
BMR is the energy you burn at rest. The formula uses age, sex, height, and weight.
Men: BMR = 10W + 6.25H − 5A + 5
Women: BMR = 10W + 6.25H − 5A − 161
Where:
- W = weight (kg)
- H = height (cm)
- A = age (years)
Step 2: Convert BMR to Maintenance Calories
Maintenance calories estimate total daily burn by multiplying BMR by an activity factor.
| Activity level | Multiplier |
|---|---|
| Sedentary (little/no exercise) | 1.2 |
| Lightly active (1–3 days/week) | 1.375 |
| Moderately active (3–5 days/week) | 1.55 |
| Very active (6–7 days/week) | 1.725 |
| Extra active (physical job / training twice/day) | 1.9 |
Step 3: Apply Your Deficit
You choose either a deficit in calories or a deficit percentage. The calculator uses:
- Deficit (calories) = maintenance × deficit % OR your entered deficit
- Daily target = maintenance − deficit
Step 4: Estimate Weight Change
To estimate weight change, the calculator converts your weekly deficit into fat-equivalent weight change.
- Weekly deficit (cal) = daily deficit × 7
- Estimated loss (lb/week) = weekly deficit / 3,500
- Estimated loss (kg/week) = weekly deficit / 7,700
This is an estimate, not a guarantee. Metabolism adapts and tracking errors are common.
How to Choose a Deficit That Works
A deficit that is too aggressive often reduces adherence and can increase hunger. A moderate deficit is usually easier to sustain and supports better training performance.
Practical deficit ranges
- 10–15% deficit: commonly sustainable for many people.
- 20–25% deficit: may work short-term, but monitor hunger, energy, and performance.
- Over 25%: often harder to maintain and increases risk of losing muscle if protein and resistance training are not solid.
Set a realistic pace
Many people do best targeting about 0.5–1.0% of body weight per week. Faster loss can happen, especially at the start, but it’s not always repeatable.
How to Use the Calculator (Step-by-Step)
- Enter your sex, age, height, and weight.
- Select your activity level that best matches your week.
- Choose a deficit method (calories or percentage).
- Review your maintenance calories, daily target, and estimated weekly loss.
- Track average intake and body weight for 2–4 weeks, then adjust by 100–200 calories if needed.
Real-Life Example #1: Desk Job to Consistent Fat Loss
Sam is a 32-year-old man, 180 cm, 85 kg, and mostly sedentary. Using the calculator, he chooses a 15% deficit. The calculator estimates maintenance calories and produces a daily target that’s realistic for daily meals.
After 3 weeks, his weekly average weight loss matches the estimate closely, so he keeps the same target.
Real-Life Example #2: Training Hard but Not Losing
Priya is a 27-year-old woman, 165 cm, 70 kg, and trains 4–5 days/week. She uses a 10% deficit first and tracks intake carefully. If her average weight doesn’t move after 2–4 weeks, she lowers intake by about 100–150 calories and reassesses.
This approach keeps the deficit controlled instead of guessing wildly.
Common Mistakes (And How to Avoid Them)
- Overestimating activity: Many people pick “moderately active” when they’re closer to “lightly active.” Start conservative.
- Inaccurate tracking: Weigh food when possible. Oils, sauces, and snacks are frequent calorie sources.
- Ignoring water weight: Scale weight can swing due to salt, carbs, and sleep. Use weekly averages.
- No adjustment window: Give it 2–4 weeks, then fine-tune.
Safety Notes
Calories need to support your health, training, and recovery. If you have a medical condition, are pregnant, or have a history of eating disorders, talk with a qualified professional before using calorie deficits.
Also remember: the calculator estimates energy needs. Your best “truth” comes from consistent tracking and body-weight trends.
Frequently Asked Questions
How many calories should I eat in a deficit to lose weight?
Start with your maintenance calories, then subtract a deficit. A common starting point is 10–15% below maintenance. For example, if maintenance is 2,000 calories, a 15% deficit targets about 1,700. Adjust after 2–4 weeks based on your weekly average weight trend.
Is a calorie deficit calculator accurate?
It’s a solid estimate, not a perfect measurement. Maintenance calories can vary because of genetics, muscle mass, daily movement, and tracking accuracy. Use the result as a starting target, then refine by checking your weekly average weight and adjusting intake by 100–200 calories.
How fast should I lose weight with a calorie deficit?
Many people aim for about 0.5–1.0% of body weight per week. That pace balances fat loss with energy and adherence. Faster loss can happen, especially early, but it’s harder to sustain and may increase the risk of losing muscle if protein and training are weak.
Should I use a deficit percentage or a fixed calorie deficit?
Both work. A percentage deficit automatically scales with your maintenance calories, which is useful if your maintenance estimate changes. A fixed calorie deficit is simpler for fine-tuning, such as dropping 100–150 calories when progress stalls.
What if my weight doesn’t change after starting a deficit?
First, confirm your intake accuracy and use weekly averages. Then check your activity level and non-exercise movement, which can drop during dieting. If you still see no trend after 2–4 weeks, reduce calories by about 100–200 or increase activity slightly, and reassess.