Body Fat %
Calculator for GLP-1 Users

The scale tells you how much weight you've lost — body fat percentage tells you whether that weight was fat or muscle. This calculator uses the US Navy Method to give you an accurate reading with just a tape measure.

Body Fat % Calculator

US Navy Method — tape measure only, no calipers needed

📏 How to measure: Use a soft tape measure. Waist = at navel level, relaxed (not sucked in). Neck = below larynx, sloping slightly downward. For women, hips = widest point below waist.
Accuracy note: The US Navy Method has a margin of error of ±3–4% compared to DEXA scanning. It's most useful for tracking changes over time rather than as an absolute number. Measure consistently — same time of day, same technique — for reliable tracking.

Why body fat matters more than weight on GLP-1

The number on the scale includes fat, muscle, bone, water, and organ tissue. When you lose weight on GLP-1 medications, the goal is to lose fat mass specifically. Research shows that without adequate protein intake and resistance training, GLP-1 users can lose 25–40% of their weight loss as lean mass.

Body fat percentage separates these components — it tells you what fraction of your body is fat versus everything else. Tracking this alongside your scale weight reveals whether your program is working optimally or needs adjustment.

Ideal tracking frequency: Measure every 4–8 weeks, not daily or weekly. Body fat percentage fluctuates with hydration and doesn't change fast enough to measure more frequently. Monthly measurements show meaningful trends without noise.

Healthy body fat ranges

CategoryMenWomen
Essential fat (minimum)2–5%10–13%
Athletic6–13%14–20%
Fitness / lean14–17%21–24%
Acceptable (healthy range)18–24%25–31%
Overweight25–29%32–39%
Obese30%+40%+

FAQ

The US Navy Method is accurate to within 3–4% compared to DEXA scanning for most people. It's most useful for tracking relative changes over time. For absolute accuracy, DEXA scanning is the gold standard but requires a clinic visit.
BMI doesn't distinguish between fat and muscle. Two people with the same BMI can have very different body compositions. Body fat percentage directly measures what you're actually trying to reduce. Tracking it ensures you're losing fat — not muscle — during GLP-1 treatment.