☾ Body Fat Calculator
Estimate your body fat percentage using the US Navy method with neck, waist, and hip measurements.
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Start Free AI Coaching ✦🧬 Understanding Body Fat & Women's Health
Body fat percentage is a more accurate indicator of health than weight alone. Women naturally carry more essential fat than men to support hormonal function and reproductive health.
✦ Why do women have higher essential body fat? ↓
Women require 10–13% essential body fat for hormone production, menstrual regularity, and reproductive health. Dropping below this range can cause amenorrhea (loss of period), bone density loss, and hormonal imbalances. Men only require 2–5% essential fat.
✦ How accurate is the U.S. Navy method? ↓
The U.S. Navy method has a margin of error of approximately ±3–4% compared to DEXA scans. It is one of the most accessible and well-validated circumference-based methods. For best accuracy, measure in the morning before eating and use a flexible tape measure.
✦ Does body fat change during my menstrual cycle? ↓
Your actual fat mass doesn't change significantly within a cycle, but measurements can appear to fluctuate due to water retention. During the luteal phase (after ovulation), progesterone causes the body to retain more water, which can make circumference measurements larger. Measure consistently during the same phase for tracking.
✦ How does the US Navy method compare to DEXA scans? ↓
The US Navy circumference method has a standard error of ±3–4% compared to DEXA (dual-energy X-ray absorptiometry), which is considered the clinical gold standard with ±1–2% accuracy. The Navy method is free and accessible, making it ideal for tracking trends over time. For a clinical baseline, a single DEXA scan costs $50–150 and gives you precise regional fat distribution.
✦ Can I lower body fat without losing muscle? ↓
Yes — this is called body recomposition. The key factors are: maintaining a moderate calorie deficit (no more than 500 kcal/day), consuming 1.6–2.2g protein per kg of body weight, prioritizing resistance training over cardio, and sleeping 7–9 hours per night. The process is slower than aggressive cutting but preserves metabolic rate and hormonal health.
✦ What body fat percentage causes period loss? ↓
There's no single cutoff — it varies by individual. However, research shows that body fat below 17–19% puts many women at risk for oligomenorrhea (irregular periods) or amenorrhea (complete cessation). The threshold depends on your personal hormonal sensitivity, energy availability, and training volume. Some female athletes maintain menstrual function at lower body fat by ensuring adequate caloric intake.
📖 How to Measure Your Body Fat
Gather a flexible tape measure and take three circumference measurements: neck, waist (at the narrowest point), and hips (at the widest point). Enter these values along with your height. The calculator uses the US Navy body fat formula validated against hydrostatic weighing.
Measure each site twice and use the average. Stand relaxed — don't flex or suck in your stomach. For tracking progress, measure at the same time of day (morning, before eating) and during the same cycle phase to minimize water-retention variability.
📊 What Your Body Fat Category Means
Women's body fat categories differ significantly from men's. Essential fat (10–13%) is the minimum required for hormonal and reproductive function. The athletic range (14–20%) reflects lean, trained physiques. Fitness (21–24%) is healthy and sustainable for most active women. Average (25–31%) is common in the general population.
Fat mass and lean mass values help you set realistic goals. During a body recomposition phase, you might see fat mass decrease while lean mass stays constant or increases — even if scale weight doesn't change much. Track these values monthly rather than weekly to see meaningful trends.
⚕️ Medical Guidance on Body Fat
Consult a physician if your body fat drops below 15% and your period becomes irregular or absent — this is a red flag for relative energy deficiency in sport (RED-S), which increases fracture risk and long-term bone density loss. On the other end, body fat above 35% is associated with higher risk of type 2 diabetes, cardiovascular disease, and chronic inflammation.