Katch-McArdle Formula Explained: Why Body Fat Percentage Matters
The Katch-McArdle formula estimates resting energy needs from lean body mass. It can be useful when body fat percentage is reasonably known.
What is the Katch-McArdle formula?
The Katch-McArdle formula is a lean-mass-based method for estimating resting calorie needs. Instead of using only height, weight, age and sex, it focuses on lean body mass.
Why lean body mass matters
Two people can have the same body weight but very different body composition. One may carry more muscle, while the other may carry more body fat. Lean mass usually needs more energy to maintain than fat mass, so body composition can affect calorie estimates.
When should you enter body fat percentage?
Enter body fat percentage if you have a reasonable estimate from a consistent method such as a professional scan, calipers used by a trained person, or a reliable long-term tracking method. It does not need to be perfect, but it should be realistic.
When should you leave it blank?
Leave it blank if you are unsure. The calculator can still use a practical general estimate from the Mifflin-St Jeor equation. A bad body-fat guess can make the result less useful.
How BMITDEE uses this field
If you enter body fat percentage, the result page explains that the estimate is based on lean body mass. If you leave it blank, the calculator uses the standard height, weight, age and sex inputs instead.
How to use the result
Whether the result uses Katch-McArdle or Mifflin-St Jeor, treat it as a starting estimate. Track your intake and weight trend for a few weeks, then adjust the calorie target if your real progress does not match your goal.
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