About this calculator
The Calorie Deficit Calculator estimates a daily calorie target for weight loss from body size, age, sex, activity level, and a chosen weekly weight-loss pace. It is useful for comparing a gentle, moderate, or more aggressive deficit before choosing a target to track in a food diary or nutrition app. The result is an educational estimate, not a prescribed diet plan.
Calorie deficit method
The calculator first estimates basal metabolic rate with the Mifflin-St Jeor equation, multiplies it by an activity factor to estimate TDEE, then subtracts the daily deficit needed for the selected weekly loss.
- male BMR = 10 x weight kg + 6.25 x height cm - 5 x age + 5
- female BMR = 10 x weight kg + 6.25 x height cm - 5 x age - 161
- TDEE = BMR x activity factor
- daily deficit = weekly loss kg x 7,700 / 7
- target calories = TDEE - daily deficit
How to use the calorie deficit calculator
- Enter your current weight in kilograms.
- Enter your height in centimetres.
- Enter your age and sex so the BMR estimate uses the correct equation.
- Choose the activity level that best describes your normal week, not your best week.
- Choose the weekly loss target you want to compare.
- Enter a goal weight if you want an estimated time-to-goal.
- Check the safety warning before using a low calorie target.
Worked examples
Moderate deficit
Input: Female, 80 kg, 175 cm, age 35, moderate activity, 0.5 kg per week loss
Calculation: Estimate BMR, multiply by 1.55 for TDEE, then subtract about 550 kcal per day.
Result: The target is roughly maintenance calories minus 550 kcal per day.
Slower loss target
Input: Same person, but 0.25 kg per week loss
Calculation: The deficit falls to about 275 kcal per day.
Result: The target calories are higher, which may be easier to sustain.
Time to goal
Input: Current weight 82 kg, goal weight 76 kg, losing 0.5 kg per week
Calculation: 6 kg to lose / 0.5 kg per week
Result: About 12 weeks before allowing for plateaus or water-weight changes.
What a calorie deficit means
A calorie deficit means eating fewer calories than the body uses over time. If the deficit is sustained, body weight usually trends down, although daily scale readings can move up and down because of water, digestion, salt, carbohydrate intake, menstrual cycle changes, and training stress.
The calculator uses the common planning estimate that about 7,700 kcal is associated with 1 kg of body fat. Real weight change is rarely that tidy, but the estimate is useful for comparing targets.
Choosing a realistic deficit
- 0.25 kg per week
- A gentle target that may suit people who want a small adjustment while keeping training, work, and hunger manageable.
- 0.5 kg per week
- A common moderate target. It usually creates a meaningful deficit without pushing calories extremely low for many adults.
- 0.75 to 1 kg per week
- A larger deficit. It may be less suitable for smaller bodies, people with high training demands, pregnancy, recovery from illness, or anyone with a history of disordered eating.
Common mistakes
The most common mistake is choosing an activity level based on occasional workouts while ignoring mostly sedentary days. Another is treating a calorie target as exact; it is a starting point that should be reviewed against real weight trends over two to four weeks.
Edge cases to watch
- Very low calorie targets can be unsuitable without medical supervision.
- People who are pregnant, breastfeeding, under 18, unwell, or recovering from an eating disorder should not use a generic deficit calculator as guidance.
- High activity jobs and endurance training can make standard activity factors less accurate.
Health and nutrition disclaimer
This calculator is for general information only and is not medical advice, dietetic advice, or a personalised weight-loss plan.
- BMR and TDEE equations are estimates.
- Food tracking errors can be large.
- Weight change can slow as body weight and activity change.
- Speak to a GP or registered dietitian if you have health concerns.
Frequently asked questions
How big should my calorie deficit be?
Many people start with a modest deficit and adjust after tracking weight trends for several weeks. A very large deficit can increase hunger, fatigue, and the chance of stopping.
Why does the calculator use 7,700 kcal per kg?
It is a common planning estimate for the energy content associated with 1 kg of body fat. Real body-weight change includes water, glycogen, gut contents, and lean mass, so it is not exact.
What if my target calories are below the warning level?
Consider choosing a slower weekly loss target. Very low calorie targets may be inappropriate without professional supervision.
Should I eat exercise calories back?
It depends on how your activity estimate was chosen. If your activity level already includes exercise, adding those calories again can double count them.
How often should I update the calculation?
Recalculate after meaningful weight change, major activity changes, or if your real progress is consistently faster or slower than expected.
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- tdee-calculator
- calorie-calculator
- macro-calculator