Body Fat Percentage Calculator (From BMI)
Use your BMI, age, and sex to estimate body fat percentage with a widely used research-based formula.
This is an estimate and not a medical diagnosis.
What this calculator does
A body fat percentage calculator from BMI gives you a quick estimate of how much of your total body weight is fat mass. Unlike BMI alone, this estimate includes age and sex, which improves usefulness for many adults. It can help you track body composition trends over time when used consistently.
The formula used
This tool uses the Deurenberg equation for adults:
Body Fat % = (1.20 × BMI) + (0.23 × Age) − (10.8 × Sex) − 5.4
- BMI is your Body Mass Index.
- Age is in years.
- Sex is coded as 1 for male and 0 for female.
Because age and sex are included, this equation is often more practical than BMI alone when estimating body composition in general populations.
How to use the body fat percentage calculator from BMI
- Enter your current BMI value.
- Enter your age in years.
- Select male or female.
- Click Calculate Body Fat %.
For the best tracking, use the same conditions each time (same time of day, similar hydration, and similar activity level before checking).
Example calculation
Adult male example
If BMI = 27 and age = 32:
Body Fat % = (1.20 × 27) + (0.23 × 32) − (10.8 × 1) − 5.4
Body Fat % = 32.4 + 7.36 − 10.8 − 5.4 = 23.6%
Adult female example
If BMI = 27 and age = 32:
Body Fat % = (1.20 × 27) + (0.23 × 32) − (10.8 × 0) − 5.4
Body Fat % = 32.4 + 7.36 − 0 − 5.4 = 34.4%
How to interpret your result
General body fat categories differ by sex:
Men
- Essential fat: 2–5%
- Athletes: 6–13%
- Fitness: 14–17%
- Average: 18–24%
- Obesity: 25%+
Women
- Essential fat: 10–13%
- Athletes: 14–20%
- Fitness: 21–24%
- Average: 25–31%
- Obesity: 32%+
These are screening ranges, not strict medical cutoffs. Always interpret with context, health history, and professional guidance.
BMI vs body fat percentage
BMI is a simple ratio of weight to height and does not directly measure fat tissue. That means muscular people may appear “overweight” by BMI, while some people with normal BMI may still carry excess fat. A body fat percentage estimate can offer better context for fitness and health planning.
Limitations to know
- This calculator is less accurate for very muscular individuals.
- It may be less reliable at very high or very low BMI values.
- It is not designed for pregnancy or certain medical conditions.
- It is intended for adults, not a pediatric diagnostic tool.
Improving body composition safely
- Follow a moderate calorie deficit if fat loss is your goal.
- Prioritize protein intake to preserve lean mass.
- Strength train 2–4 times per week.
- Use daily walking and basic cardio for energy expenditure.
- Sleep 7–9 hours and manage stress to support recovery and hormones.
FAQ
Is this calculator accurate?
It is reasonably useful for population-level estimates and personal trend tracking, but it is not as precise as DEXA, hydrostatic weighing, or clinical assessments.
Can I use this if I do not know my BMI?
Yes. First compute BMI using height and weight, then enter that value here to estimate body fat percentage.
Should I focus on body fat percent or body weight?
For many people, body fat percentage and waist measurement provide better insight than scale weight alone. Use multiple metrics and track progress over weeks, not days.