Body Fat Goal Calculator
Enter your current weight, body fat percentage, and daily calorie deficit to estimate your target weight, amount of fat you need to lose, and the time frame.
Enter key data
- lean body mass
- 60.00kg
- target weight
- 70.59kg
- Need to lose fat
- 9.41kg
The range compares the sensitivity scenario of "nearly maintaining lean body mass" versus "20% of total weight loss from lean body mass."
How to understand the result
It is a mathematical result obtained by inverting the target body fat percentage and assuming that the lean body mass remains unchanged.
Changes in lean body mass, fluids, and energy expenditure can all skew true progress away from the static formula.
A 1-2 percentage point change in body fat percentage input may significantly change the target weight and estimated time.
Learn more
Formulas and Assumptions
The calculation only applies to a simplified scenario where the target body fat percentage is lower than the current body fat percentage, the daily caloric deficit is greater than 0, and lean body mass is basically maintained. 7700 kcal/kg is an easy-to-understand energy conversion, not an accurate long-term rule.
Example calculation
- The current weight is 80 kg, the current body fat rate is 25%, and the lean body mass = 80 × (1 − 0.25) = 60 kg.
- Target body fat percentage is 15%, target weight = 60 ÷ (1 − 0.15) ≈ 70.59 kg.
- The amount of fat to be lost is about 9.41 kg; based on static conversion of 500 kcal/day, the time is about 9.41 × 7700 ÷ 500 ≈ 145 days.
Lean body mass loss scenario table
The table below uses "the ratio of lean body mass loss to total weight loss" as a sensitivity parameter and does not represent a recommended target or a proportion that will inevitably occur.
| Scenario | target weight | Estimate fat changes | estimated time |
|---|---|---|---|
| Lean body mass basically maintained | 70.59kg | 9.41kg | 145 days |
| 10% of weight loss comes from lean body mass | 69.33kg | 9.60kg | 148 days |
| 20% of weight loss comes from lean body mass | 67.69kg | 9.85kg | 152 days |
Usage boundaries and disclaimers
- This tool is not suitable for fat gain goals, target body fat percentage is not lower than the current body fat percentage, or the daily caloric deficit is 0.
- Changes in weight and body fat are not linear over time; metabolic adaptation, exercise volume, diet execution, body fluids, and measurement error can all affect results.
- It is not suitable for pregnant women, minors, and people with or suspected eating disorders; those with lower target body fat or larger caloric deficits should seek professional evaluation.
- Results are for general health management reference only and are not intended for diagnosis, treatment, nutritional prescription or substitute medical advice.
FAQ
Why may actual fat loss take longer than results?
Because weight changes are typically not linear over time, energy expenditure, activity level, body fluids, and lean body mass may all change. 7700 kcal/kg is only a static approximation, and the longer the time, the greater the error usually.
Why is the target weight not the current weight directly minus the difference in body fat percentage?
Body fat percentage is the ratio of fat mass to total body weight. The target weight needs to be estimated first, and then the target body fat percentage is used to calculate the target weight, rather than directly subtracting the percentage.
Will body fat percentage measurement error affect the results?
Yes. Home body fat scales, girth measurements, and skinfold methods can all be affected by moisture, measurement time, and method. Input errors directly change target weight and time estimates.
Can this result be used to formulate a very low-calorie diet?
Not recommended. This tool only makes mathematical estimates and does not provide dietary prescriptions. Larger caloric deficits or lower target body fat should be evaluated by a physician or registered nutrition professional.
Who should not use this calculator?
Pregnant women, minors, people with existing or suspected eating disorders, and people in need of medical nutritional treatment should not rely on this tool to develop a fat loss plan.
Related tools
Tool information, source and update time
Privacy and local processing:Input and calculations are processed only within the current browser, no cookies are uploaded, cookies are used, and weight or body fat data is not saved. When copying a sharing link, the URL parameters will be written into the input. Please confirm the recipient before sharing.
Calculation implementation:It is independently implemented using native JavaScript and does not introduce third-party computing libraries; the core functions do not rely on remote APIs or CDNs.
Dynamic model reference:National Institute of Diabetes and Digestive and Kidney Diseases: Body Weight Planner, used to understand the dynamic relationship between energy gaps and weight changes.
7700 kcal/kg limit reference:Thomas et al.: Time to Correctly Predict the Amount of Weight Loss with Dieting;Heymsfield et al.: Energy Content of Weight Loss.
Content and formula proofreading:.