A calorie deficit is the gap between your maintenance calories and the calories you eat.
Use this formula:
Calorie deficit = maintenance calories - calories eaten
A practical starting point for many adults is to eat 300 to 500 fewer calories than maintenance calories per day. A larger deficit is not automatically better. The CDC recommends gradual weight loss of about 1 to 2 pounds per week because it is more likely to be maintained than faster weight loss.
Calorie Deficit Calculation at a Glance
| Step | Calculation | Example |
|---|---|---|
| 1. Estimate resting calorie needs | Mifflin-St Jeor equation | 1,830 calories |
| 2. Estimate maintenance calories | Resting needs x activity factor | 2,837 calories |
| 3. Choose a deficit | Maintenance calories - 300 to 500 | 2,337 to 2,537 calories |
| 4. Check your trend | Use weekly weight averages | Adjust if needed |
Step 1: Calculate Your Resting Calorie Needs
Your resting metabolic rate, or RMR, estimates how many calories your body uses at rest. The Mifflin-St Jeor equation uses body weight, height, age and sex to estimate RMR.
The original equation was developed from measurements of 498 healthy adults.
Convert your measurements first:
- Kilograms: pounds / 2.205
- Centimeters: inches x 2.54
Mifflin-St Jeor Equations
For men:
RMR = (10 x weight in kg) + (6.25 x height in cm) - (5 x age) + 5
For women:
RMR = (10 x weight in kg) + (6.25 x height in cm) - (5 x age) - 161
These equations provide an estimate, not a laboratory measurement. Actual calorie needs can vary with muscle mass, genetics, medical conditions, medication, sleep and daily movement.
Step 2: Estimate Your Maintenance Calories
Maintenance calories are also called total daily energy expenditure, or TDEE. TDEE includes resting metabolism, walking, exercise, digestion and other daily activity.
Use this calculation:
Estimated maintenance calories = RMR x activity factor
| Activity level | Common multiplier | Description |
|---|---|---|
| Sedentary | 1.2 | Little planned exercise and mostly sitting |
| Lightly active | 1.375 | Light exercise 1 to 3 days per week |
| Moderately active | 1.55 | Moderate exercise 3 to 5 days per week |
| Very active | 1.725 | Hard exercise 6 to 7 days per week |
| Extremely active | 1.9 | Very demanding physical work and frequent training |
Choose the category that reflects your average week. If your multiplier includes exercise, do not add all of those exercise calories again. That can lead to double counting.
Worked Calorie Deficit Example
Suppose a 40-year-old man weighs 90 kilograms and is 180 centimeters tall.
1. Calculate RMR
RMR = (10 x 90) + (6.25 x 180) - (5 x 40) + 5
RMR = 1,830 calories per day
2. Estimate Maintenance Calories
If he is moderately active:
TDEE = 1,830 x 1.55
TDEE = approximately 2,837 calories per day
3. Apply a Deficit
A 300 to 500 calorie deficit gives this target range:
2,837 - 300 = 2,537 calories
2,837 - 500 = 2,337 calories
His starting weight-loss target would be about 2,337 to 2,537 calories per day.
How Large Should Your Calorie Deficit Be?
A suitable starting point depends on your maintenance calories, appetite and ability to maintain the plan.
- 250 to 300 calories per day: A smaller gap that may be easier to maintain
- 300 to 500 calories per day: A common starting range for many adults
- 500 to 750 calories per day: A faster rate that may suit some people with higher maintenance needs
- Around 1,000 calories per day: A more aggressive approach that requires care, particularly if it leaves you short on nutrients
Older weight-loss guidance often uses a 500 to 1,000 calorie daily deficit as a rough target for 1 to 2 pounds of weight loss per week. The traditional "3,500 calories equals one pound" rule is only an approximation. Weight loss changes over time as body weight, appetite, activity and metabolic rate change.
The NIDDK Body Weight Planner can provide another estimate. It creates a calorie and activity plan that accounts for changes during weight loss. It is intended for adults and is not designed for people under 18 or those who are pregnant or breastfeeding.
How Do You Know if Your Calorie Target Is Correct?
A calorie calculator gives you a starting estimate. Your weight trend gives you a better indication of your actual maintenance level.
Use this process:
- Choose a daily calorie target.
- Follow it consistently for about 2 to 3 weeks.
- Weigh yourself under similar conditions, preferably in the morning.
- Calculate a weekly average instead of reacting to one weigh-in.
- Adjust the target only if the trend is different from what you expected.
If your average weight is not falling after 2 to 3 consistent weeks, you can:
- Reduce intake by approximately 100 to 200 calories per day, or
- Add a manageable amount of walking or other activity.
If your weight is dropping very quickly, you feel persistently fatigued or hunger is difficult to manage, increase calories modestly and consider speaking with a registered dietitian or healthcare professional.
Daily weight changes do not necessarily reflect fat loss. Water retention, carbohydrate and sodium intake, bowel contents, exercise and the menstrual cycle can all affect your weight from one day to the next.
Should You Create the Deficit Through Food or Exercise?
You can use both. For many people, reducing food intake creates most of the deficit, while exercise supports health, fitness and weight maintenance.
The CDC explains that reducing food intake and increasing physical activity together creates the calorie deficit responsible for weight loss. It also recommends that adults complete at least 150 minutes of moderate-intensity aerobic activity per week and muscle-strengthening activity on at least 2 days per week for general health.
A practical approach is to:
- Reduce high-calorie drinks, alcohol and frequent snacks.
- Keep portions consistent.
- Build meals around protein-rich foods, vegetables, fruit, whole grains and legumes.
- Walk more during the day.
- Perform resistance training to support strength while losing weight.
- Avoid assuming that exercise calories can always be measured or eaten back accurately.
Common Calorie Deficit Calculation Mistakes
Using BMR as Your Calorie Target
Your RMR or BMR is not your maintenance intake. It estimates the energy your body uses at rest. Maintenance calories also include movement and activity.
Choosing an Activity Level That Is Too High
If you exercise occasionally but sit for most of the day, choosing "very active" may overestimate your maintenance calories. Start with a conservative category and compare the estimate with your weight trend.
Treating the Estimate as Exact
Even a well-designed equation can only estimate energy expenditure. Your target may need adjustment based on what happens over several weeks.
Trying to Lose Weight as Quickly as Possible
A larger deficit can increase hunger, fatigue and the difficulty of maintaining the diet. Gradual weight loss is generally easier to sustain than extreme restriction.
Ignoring Medical Circumstances
Speak with a healthcare professional before creating a calorie deficit if you are:
- Pregnant or breastfeeding
- Under 18
- Taking diabetes medication
- Managing a medical condition
- Recovering from an eating disorder
- Experiencing unexplained weight changes
The Simplest Answer
Estimate your maintenance calories, subtract 300 to 500 calories, and follow the target for 2 to 3 weeks. Use your average weight trend to decide whether the target is working or needs a small adjustment.