Calorie Deficit Calculator
What is a Calorie Deficit Calculator?
Weight loss happens when you consistently eat fewer calories than your body burns. A calorie deficit calculator works out your maintenance calories (TDEE) and then subtracts the deficit you choose, giving you a realistic daily calorie target and the weight loss pace you can expect.
A full run shows how the pieces connect. A 40-year-old man, 180 cm and 90 kg, with a desk job and little exercise has a Mifflin-St Jeor BMR of about 1,830 calories. The sedentary factor of 1.2 puts maintenance near 2,196. Choosing the moderate pace subtracts 500, giving a target of roughly 1,696 calories a day and an expected loss of about 2 kg per month. The mild pace would target 1,946 for slower, easier loss, while the aggressive 750-calorie cut lands at 1,446 - still above his BMR here, but a level many smaller people could not sustain safely.
Six inputs set the plan: age, gender, height, weight and activity level, plus your chosen pace of loss - mild, moderate or aggressive. The calculator computes BMR from the Mifflin-St Jeor equation, multiplies by the activity factor to get maintenance calories, and subtracts the deficit that matches your pace: 250, 500 or 750 calories a day. Results show your daily target, your maintenance level for reference, and the expected loss per week and per month, using the standard conversion of about 7,700 calories per kilogram of body fat.
The calculator fits people starting a first deliberate cut, restarting after a plateau, or checking whether an app-generated target is sane. Its assumptions deserve respect: the 500-calorie rule is an average that blurs as you get lighter, metabolic adaptation can shrink the deficit your body actually experiences, and calorie tracking carries measurement error in both directions. The formula cannot see muscle mass, medical conditions or medications. Eat at or above your BMR, prioritize protein and resistance training to protect muscle, and recalibrate the target every 2-3 kilograms of progress rather than trusting one number for months.
Frequently Asked Questions
What is the best calorie deficit for weight loss?
A moderate deficit of 300-500 calories below maintenance is sustainable for most people and preserves muscle. Very large deficits (over 750 calories) are hard to maintain and can slow your metabolism. Aim for 0.25-0.75 kg per week, which this calculator supports directly.
How much weight will I lose in a month?
On a 500-calorie daily deficit you can expect roughly 2 kg (about 4.4 lb) per month, assuming you track calories accurately. Real results vary with adherence, water weight and exercise - treat the figure as a guideline, not a guarantee.
Do I need to eat below my BMR to lose weight?
No. Your BMR is the energy needed to keep you alive at rest; going below it for long periods can cause muscle loss, fatigue and a slower metabolism. Choose a deficit that keeps your target at or above your BMR.
Should I combine a deficit with exercise?
Exercise helps by increasing the calories you burn and preserving muscle, but nutrition drives most of the deficit. Combining a modest deficit with strength training is the most effective way to lose fat while keeping lean mass.
What deficit is needed to lose 1 pound a week?
Roughly 500 calories a day, since a pound of body fat stores about 3,500 calories and the deficit accumulates daily. The calculator translates that pace into your personal target by subtracting 500 from your maintenance calories. Faster paces work for some people but are harder to sustain.
Why did my weight loss stop on the same calories?
Several forces converge as you diet: a smaller body burns less, everyday movement tends to drop, and metabolic adaptation trims the effective deficit. The fix is usually a recalculation at your current weight, a 100-200 calorie adjustment, or a short diet break at maintenance.