Fat Loss and Muscle Change Calculator

By | February 13, 2004


This fat loss and muscle change calculator helps you determine how much fat you’ve lost and your change in lean mass by entering start and end weights, along with start and end body fat percentages.

Muscle Change and Fat Loss Calculator

Enter your beginning weight in pounds:
Enter your ending weight in pounds:
Enter your beginning body fat as a decimal:
Enter your ending body fat as a decimal:
Your beginning fat

Weight * Bodyfat
Your beginning lean:

Weight – Fat
Your ending fat:
Your ending lean:
Fat difference:
Lean difference:

Tracking Body Composition is Key!

Many people know that tracking weight on the scale is not as important as tracking body composition. Body composition refers to the amount of fat and lean mass you are carrying. Lean mass includes muscle, skeletal tissue, water, and other non-fat mass in your body.

If you were to lose 3 pounds on the scale, would that be successful?

It depends.

  • One person may lose 5 pounds of fat and gain 2 pounds of muscle.
  • Another might lose 1.5 pounds of fat and 1.5 pounds of muscle.

Who do you think looks better in the end?

It is important to note that not only is body fat testing not 100% accurate, but lean mass does not mean just muscle. Many people get concerned when they see they lost 3 pounds of lean mass or get excited when they see a gain of 3 pounds of lean mass. In reality, most rapid gains or losses are water weight!

Shifts in Fluid Weight

When someone begins a new nutrition and/or exercise regimen, it is not uncommon for shifts in fluid balance due to changes in sodium and potassium intake, as well as reduction of carbohydrate intake, to take place. Most of this lean mass loss is water and NOT muscle! On the other hand, if you suddenly consume a large amount of carbohydrate, carbohydrate bonds to water when it enters the cell, so you may gain a significant amount of water weight.

Creatine also pulls water into the cell, and it is not uncommon to gain 5 – 7 pounds in the first week of creatine supplementation! Is this muscle? No! But is it useful weight? Certainly. A cell packed with fluid is volumized and provides more leverage and strength, which in turn allows more workload to stress the muscle and provide for further growth.

So, use this tool to track your progress, but focus more on the fat changes and remember that no one can really tell you if the lean mass changes are due to muscle or water!

One thought on “Fat Loss and Muscle Change Calculator

  1. Anita

    I have begun to beleive that most “fitness professionals” and consumers of their products have lost touch with common sense. If our body consumed muscle BEFORE fat when food supply was low, the human race would have died out long ago. Our ancestors would have been too weak to go out in search of food. We are told over and over that fat is our body’s energy storage system for times of famine… and then told that the same body will start canobalizing it’s muscle if we miss a meal. I don’t get it!

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