Why does my smart scale give a different number?
Smart scales use Bioelectrical Impedance Analysis (BIA), which estimates fat based on how water conducts electricity in your body. If you are dehydrated, have calluses on your feet, or ate a salty meal, the number can swing wildly. The US Navy method (tape) is generally more consistent for tracking trends because it measures physical geometry, not electrical conductivity.
Can I spot reduce fat from my belly?
No. 'Spot reduction' is a myth. When you lose body fat, your body decides where to take it from based on genetics and hormones. You cannot target belly fat by doing crunches. However, reducing overall body fat will eventually reduce belly fat.
What is a good body fat percentage for my age?
Acceptable ranges shift up slightly with age. For a 20-39 year old man, 8-19% is healthy. For a 40-59 year old man, 11-21% is healthy. For women 20-39, 21-32% is healthy, and for 40-59, 23-33% is healthy. The calculator provides specific category guidance based on your inputs.
How often should I measure?
Once a week is ideal. Measuring daily is discouraged because normal water weight fluctuations can be discouraging. Pick a consistent day (e.g., Friday morning) and stick to it.
Does muscle weigh more than fat?
A pound of muscle weighs the same as a pound of fat, but muscle is much more dense. One pound of muscle takes up about 18% less space than one pound of fat. This is why you can look smaller and leaner (lose inches) even if your weight on the scale stays the same.
Is the BMI method or Navy method better?
For most active people, the Navy method is better. BMI is a simple height-to-weight ratio and penalises people with muscle. The Navy method accounts for your shape, giving credit for a slim waist and broad shoulders/hips.
What if I don't have a tape measure?
You can use a piece of string or a phone charging cable. Wrap it around the body part, mark the spot with your finger, and then lay it flat against a ruler or construction tape measure to get the number.
Why do women need more essential fat than men?
Women require higher essential fat levels (10-13% vs 2-5%) to support reproductive hormones and menstrual cycle function. Dropping below this level can cause serious long-term health issues like osteoporosis and infertility.
Can I use this calculator if I am pregnant?
No. The formulas are not designed for pregnancy. The abdominal measurements will be skewed by the baby, and BMI is not a valid metric during pregnancy. Consult your obstetrician for appropriate weight gain guidelines.
How do I calculate my lean body mass?
This calculator does it for you! Lean Body Mass = Total Weight - (Total Weight × Body Fat %). For example, if you weigh 200 lbs and have 20% body fat, you have 40 lbs of fat and 160 lbs of lean mass.