Calorie Deficit Calculator
Estimates only. The Mifflin-St Jeor formula is one of the most validated BMR equations, but real-world results vary with body composition, hormones, and daily routine.
A calorie deficit means eating fewer calories than your body burns. To calculate yours, find your maintenance calories (TDEE), choose a daily deficit of 250 to 1,000 calories, and subtract it from TDEE to get your daily target. A 500-calorie daily deficit equals roughly 1 pound of fat loss per week.
How the Calorie Deficit Calculator Works
This calculator estimates your numbers in three stages. First, it estimates your basal metabolic rate (BMR) with the Mifflin-St Jeor equation, one of the most validated formulas in nutrition science. Second, it multiplies BMR by your activity level to get your total daily energy expenditure (TDEE), which is the number of calories that maintains your current weight. Third, it subtracts your chosen weekly goal (times 500 calories per pound) from TDEE to give your daily calorie target and your daily deficit.
How to Calculate Your Calorie Deficit in 5 Steps
- Measure your height and weight. Enter them in metric or imperial units. Weigh yourself in the morning, before eating, for the most consistent number.
- Enter your age and sex. BMR declines with age, and the formula adjusts for the metabolic differences between men and women.
- Pick your activity level honestly. Most people overestimate this. If you have a desk job and walk a few times a week, choose lightly active, not moderately active.
- Choose a weekly weight-loss goal. Options range from 0.5 to 2 pounds per week. A 1-pound weekly goal is a 500-calorie daily deficit and is a sustainable middle ground for most adults.
- Read your results. The calculator shows your BMR, TDEE, daily calorie target, daily deficit, and projected weekly loss. If your target falls below 1,200 calories (women) or 1,500 calories (men), you will see a friendly warning to check with a professional before proceeding.
The Formulas Behind the Calculator
The calculator uses the Mifflin-St Jeor equations:
- Men: BMR = 10 x weight (kg) + 6.25 x height (cm) - 5 x age + 5
- Women: BMR = 10 x weight (kg) + 6.25 x height (cm) - 5 x age - 161
Then TDEE = BMR x activity multiplier (1.2 sedentary up to 1.9 extra active). Finally, daily target = TDEE - (weekly goal in pounds x 500), because one pound of body fat stores roughly 3,500 calories.
Verified Example Calculations
These two examples were run through the calculator logic and verified:
| Person | BMR | TDEE | Goal | Daily Target | Daily Deficit |
|---|---|---|---|---|---|
| Male, 35, 80 kg, 180 cm, moderately active | 1,755 | 2,720 | 1 lb/week | 2,220 | 500 |
| Female, 30, 70 kg, 165 cm, lightly active | 1,420 | 1,953 | 0.5 lb/week | 1,703 | 250 |
Walkthrough for the first example: BMR = 10 x 80 + 6.25 x 180 - 5 x 35 + 5 = 800 + 1,125 - 175 + 5 = 1,755. TDEE = 1,755 x 1.55 = 2,720.25, displayed as 2,720. Goal of 1 lb/week gives a 500-calorie deficit, so the target is 2,720 - 500 = 2,220 calories per day.
Choosing a Safe Deficit Size
A deficit of 250 to 500 calories per day suits most people. That produces 0.5 to 1 pound of fat loss per week, a rate most guidelines describe as safe and sustainable. Larger deficits of 750 to 1,000 calories per day can work for people with more weight to lose, but they raise the risk of muscle loss, fatigue, and nutrient gaps. As a floor, most adults should not eat below 1,200 calories per day (women) or 1,500 calories per day (men) without professional supervision.
Learn More
These guides explain every piece of the process in detail:
- How to Calculate a Calorie Deficit
- How Many Calories Should I Eat to Lose Weight?
- What Is TDEE and How Do You Calculate It?
- How Fast Can You Safely Lose Weight?
- BMR vs TDEE: What Is the Difference?
Frequently Asked Questions
How many calories is a 1-pound-per-week deficit?
One pound of body fat stores roughly 3,500 calories, so losing 1 pound per week requires a total deficit of 3,500 calories per week, which is 500 calories per day. You create this by eating 500 fewer calories than your TDEE, by burning 500 extra calories through activity, or by combining both.
Should I use my BMR or TDEE to set my deficit?
Use TDEE. BMR only covers the calories your body burns at rest, so it ignores everything you do during the day. TDEE includes your activity, which makes it your true maintenance level. Subtracting your deficit from TDEE gives a realistic daily target.
Can I eat below my BMR?
Eating below BMR is generally not advised without supervision. BMR covers the energy your organs need to function at rest. Consistently eating less can cause fatigue, hormonal disruption, and muscle loss. Most people get the best results with a target between BMR and TDEE.
Why am I not losing weight in a deficit?
The most common reasons are tracking errors, overestimated activity levels, water retention masking fat loss, and metabolic adaptation over long dieting periods. Try weighing food for a week, picking one activity level lower in the calculator, and watching the two-week trend instead of daily scale readings.
Does the 3,500-calorie rule always hold?
It is a useful approximation, not a law. Real fat loss varies with body composition, how long you have been dieting, and how much of the lost weight is water or lean tissue. Short-term results often follow the rule closely, while long-term loss usually slows as your body adapts.
Is a calorie deficit calculator accurate?
It gives a strong starting estimate, usually within 10 to 15 percent of your true needs. The Mifflin-St Jeor formula is well validated, but individual factors like muscle mass and daily routine change the real number. Treat the result as a starting point, then adjust by 100 to 200 calories every two weeks based on your actual weight trend.