Calculator inputs
Use the responsive grid below. Large screens show three columns, smaller screens show two, and mobile shows one.
Formula used
This calculator treats weight loss as an energy-balance problem. In physics terms, stored body mass changes when energy intake differs from energy use. A common planning approximation is that 1 kilogram of body mass corresponds to about 7,700 kilocalories.
1) Basal metabolic rate
Mifflin-St Jeor
Men: BMR = 10W + 6.25H − 5A + 5
Women: BMR = 10W + 6.25H − 5A − 161
Revised Harris-Benedict
Men: BMR = 88.362 + 13.397W + 4.799H − 5.677A
Women: BMR = 447.593 + 9.247W + 3.098H − 4.330A
Katch-McArdle
BMR = 370 + 21.6 × Lean Body Mass (kg)
Lean Body Mass = Weight × (1 − Body Fat % / 100)
2) Total daily energy expenditure
TDEE = BMR × Activity Factor
3) Daily calorie target for fat loss
Daily Deficit = (Weekly Loss Target × 7700) / 7
Target Calories = TDEE − Daily Deficit
4) Estimated timeline
Weeks to Goal = Weight to Lose / Weekly Loss
These formulas are planning estimates. Real results vary with adherence, water balance, muscle change, hormones, medication use, and measurement error.
How to use this calculator
- Select metric or imperial units.
- Enter sex, age, height, and current weight.
- Enter a lower goal weight.
- Choose your average activity level.
- Select a BMR equation. Use Katch-McArdle only when body fat is known.
- Set your desired weekly loss pace.
- Press the calculate button.
- Review your maintenance calories, target calories, deficit, weekly loss, and projected goal date.
- Use the CSV and PDF buttons to export the result summary.
Example data table
| Profile | Weight | Height | Activity | Maintenance | Goal Intake | Weekly Loss |
|---|---|---|---|---|---|---|
| Office worker | 85 kg | 175 cm | 1.20 | 2,230 kcal | 1,680 kcal | 0.50 kg |
| Active student | 72 kg | 170 cm | 1.55 | 2,420 kcal | 1,870 kcal | 0.50 kg |
| Gym trainee | 95 kg | 182 cm | 1.725 | 3,040 kcal | 2,490 kcal | 0.50 kg |
| Imperial example | 187 lb | 5 ft 9 in | 1.375 | 2,480 kcal | 1,980 kcal | 1.00 lb |
Frequently asked questions
1) Why is this called a physics-style weight loss calculator?
It uses the energy-balance idea from physics. Body mass changes when energy in and energy out differ over time. The calculator converts that energy gap into an estimated fat-loss pace and timeline.
2) What does maintenance calories mean?
Maintenance calories estimate how much energy you use in a day while holding body weight steady. Eating near that value should keep weight roughly stable when activity and body composition remain similar.
3) Why does the calculator use 7,700 kcal per kilogram?
It is a common planning approximation for converting stored body mass into energy. Real human weight change is not perfectly linear, but this rule is useful for practical forecasting and calorie budgeting.
4) Which formula should I choose?
Mifflin-St Jeor is a popular general-purpose choice. Revised Harris-Benedict is another classic estimate. Katch-McArdle can be useful when you know body fat percentage, because it accounts for lean mass directly.
5) Why did my calorie target increase automatically?
If your requested pace created an extremely low intake, the calculator raised calories to a conservative floor. That helps avoid unrealistic outputs and produces a safer planning estimate for most adults.
6) Are these results exact?
No. Daily energy use changes with stress, sleep, hormones, hydration, exercise quality, body composition, and tracking accuracy. Use the result as a starting estimate, then adjust after monitoring real progress.
7) Can I use this for weight gain or maintenance?
This page focuses on losing weight. However, the maintenance value is still useful. You can use it as a baseline and add or subtract calories depending on whether you want maintenance, gain, or loss.
8) Should I rely only on this calculator for health decisions?
No. This tool is educational and should not replace professional care. People with medical conditions, pregnancy, eating disorders, or medication-related weight changes should seek personalized guidance from a qualified clinician.