Want to know how much fat you have to lose — or how much lean mass you carry?
You’re in the right place. This calculator will help you estimate both.

⚠️ AssumptionS (And Why They May Not Hold For You)

1. Lean body mass is assumed to stay constant during weight loss.

This means all of the energy burned to fuel your calorie deficit comes from fat tissue, not muscle mass. That’s likely to hold true if you:

• Train hard and consistently (see our free training programs),
• Lose weight at an appropriate pace (~0.5–0.75% of body weight per week), and
• Eat enough protein.

That said, while optimal muscle growth doesn’t happen in a calorie deficit, you can still gain some muscle — especially if you’re relatively new to training, losing weight slowly, or coming from a suboptimal diet. Just don’t expect those gains to offset fat loss in a noticeable way.

2. No other weight loss is accounted for, which isn’t realistic.

If you have ever dieted before, you probably saw a rapid drop on the scale. That initial “whoosh” was mostly water, gut content, and glycogen — not fat.

For example, if you lost 8 pounds in the first two weeks but then averaged 1 pound per week after, only ~2 pounds of that initial drop was fat. The other 6 pounds were from non-fat sources.

So, if you lost 8 pounds in the first two weeks but then 1 pound every week after, your fat loss in those first two weeks was 2 pounds, and your water, gut content, and glycogen losses were 6 pounds.

So, to reach your target body fat percentage, you’ll likely need to lose more than the calculator shows — often by 5–6 pounds. But don’t worry: you’ll regain that weight (in water, glycogen, and gut content) once you return to maintenance calories.

The Fat Loss Calculator’s Equations

Lean Body Mass = Current Weight × (1 - Current Body Fat Percentage ÷ 100)

Example: If someone weighs 180 lbs with 20% body fat:

• Lean Body Mass = 180 × (1 – 20 ÷ 100) = 180 × 0.8 = 144 lbs

Target Weight = Lean Body Mass ÷ (1 - Target Body Fat Percentage ÷ 100)

Example: Using the same person who wants to reach 15% body fat:

• Target Weight = 144 ÷ (1 – 15 ÷ 100) = 144 ÷ 0.85 = 169.4 lbs

Weight to Lose = Current Weight - Target Weight

Example: Continuing with our example:

• Weight to Lose = 180 – 169.4 = 10.6 lbs

Next Steps

Now that you have calculated how much weight you have to lose to get to your target.

1. Use our Calorie and Macro Calculator.
2. Enter your email address in the box below to get our free Transformation Kickstart Bundle.