How the calorie deficit estimate is worked out
The Mifflin-St Jeor equation estimates resting energy needs. Activity and conservative limits then determine the daily target.
BMR = 10W + 6.25H − 5A + 5 (men) or − 161 (women); maintenance = BMR × activity; target = maintenance − guarded deficit
- Convert weight to kilograms and height to centimetres. Use age and sex in the Mifflin-St Jeor equation.
- Multiply BMR by the activity factor: sedentary 1.2, light 1.375, moderate 1.55, very active 1.725 or extra active 1.9.
- Estimate the requested daily deficit using 7,700 kcal per kg or 3,500 kcal per lb, divided across 7 days.
- Cap the deficit at 25% of maintenance. Keep the daily target at or above 1,500 kcal for men or 1,200 kcal for women.
- Estimate weekly loss and time from the final deficit. Do not give deficit targets for underweight BMI or ages outside 18 to 80.
Worked example: A man aged 35, weighing 80 kg and 180 cm tall, has an estimated BMR of 1,755 kcal. Moderate activity gives about 2,720 kcal maintenance. A requested 0.5 kg weekly loss implies 550 kcal daily deficit and a target of about 2,170 kcal. The simple estimate is 10 weeks for 5 kg, but actual loss varies.
Example adult profiles
| Formula | Age | kg | cm | Activity | Goal | Maintenance calories (TDEE) | Target daily calories | Daily deficit |
|---|---|---|---|---|---|---|---|---|
| Male | 35 years | 80 kg | 180 cm | Moderate | 0.5 kg per week | 2,720 kcal | 2,170 kcal | 550 kcal |
| Female | 30 years | 65 kg | 165 cm | Light | 0.5 kg per week | 1,884 kcal | 1,413 kcal | 471 kcal |
Swipe the table sideways to see the rest.
Metric examples only. These are estimates, not recommended intakes for everyone with similar measurements.
Things to consider
- Choose activity based on your usual routine, not an unusually busy day.
- The expected pace uses the final deficit after safety limits.
- Do not count exercise twice. It is already part of the activity estimate.
- Calorie floors are guardrails, not a guarantee that a target is right for you.
Frequently asked questions
What is a calorie deficit?
A calorie deficit means taking in less energy than your body uses. Over time this can lead to weight loss, but the amount and rate vary between people.
How big should a calorie deficit be?
A moderate pace is generally preferable. About 0.5 kg per week is common guidance, but it is not suitable for everyone. This calculator caps the deficit at 25% of maintenance and may suggest a slower pace.
Why is 7,700 kcal per kg only an estimate?
It is a rough energy model, not a prediction of body-weight change. Water, body composition and changing energy needs affect results. Real weight loss often slows over time, so the time estimate is not a deadline.
What are the minimum safe calories?
There is no single minimum that is safe for everyone. This calculator uses floors of 1,500 kcal for men and 1,200 kcal for women and never recommends eating below them. A higher intake may be needed. Lower intakes require medical supervision.
Does exercise count towards a calorie deficit?
Yes. Exercise contributes to energy use and is included in the activity factor. Do not add the same exercise calories again. Activity estimates and wearable calorie readings can be inaccurate.
When should I see a professional?
Talk to a GP or dietitian before changing how you eat, especially during pregnancy or breastfeeding, with a health condition or a history of disordered eating. Children, teens and people in the underweight BMI range should not use this tool to plan a deficit.
Results are estimates for general information only, not financial, medical or professional advice.