Body Recomposition Calculator

What Is Body Recomposition? (And Why The Scale Lacks Context)

Most traditional diet advice forces you to choose between cutting (losing fat) or bulking (gaining muscle). A body recomposition calculator helps you find the balance to do both.

Body recomposition—often shortened to "recomp"—is the athletic equivalent of having your cake and eating it too. It involves losing body fat and gaining lean muscle mass at the same time. It’s not magic; it’s just multitasking for your metabolism.

While the bathroom scale might barely budge during a recomp, your body’s internal architecture is undergoing a massive renovation. A pound of fat takes up roughly 18% more space than a pound of muscle (check out our guide on muscle vs. fat density). So, you can weigh exactly the same but look leaner, fit into smaller clothes, and burn more calories just sitting on the couch.

Who Is This For?

You don't need to be a pro athlete to benefit from recomposition. This approach works best for:

1. "Skinny Fat" Individuals: You’re at a healthy weight but feel "soft" due to lower muscle tone. (Read more: What is Skinny Fat?)
2. DEXA Scan Users: You’ve got your precise Lean Mass vs. Fat Mass numbers from a BodySpec scan and want to put them to work.
3. Returning Athletes: You used to train hard and are counting on "muscle memory" to bounce back.
4. Fitness Enthusiasts: You want to break a plateau without suffering through a miserable diet phase.
5. Healthy Agers & Menopausal Women: You want to preserve muscle mass while navigating metabolic shifts or hormonal changes. (See: Menopause Weight Gain Solutions)

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How to Get the Best Results From This Calculator

1. Choose Your Formula

Garbage in, garbage out—accuracy depends on your inputs. We use two main scientific models:

• Mifflin-St Jeor (Standard): Use this if you don't know your body fat percentage. It estimates your basal metabolic rate (BMR) using height, weight, and age. For a measurement rather than an estimate, consider booking an RMR Test with BodySpec.
• Katch-McArdle (Precise): The gold standard for BodySpec clients. Because it calculates based on Lean Body Mass (LBM) rather than total weight, it doesn't get confused by extra body fat or high muscle mass. If you have scan results, toggle this on for the most accurate starting point.

2. Be Honest About Your Activity

It's tempting to click "Athlete," but overestimating how much you move is the #1 reason recomposition stalls.

• Pro Tip: "Moderately Active" usually implies 3–5 intense workouts a week plus an active lifestyle. If you crush it in the gym for an hour but sit at a desk for the other 23, stick to "Lightly Active" and let the specific training day calorie bumps handle your workout fuel.

3. The Strategy: Calorie Cycling

To build muscle and burn fat simultaneously, you need to be strategic with fuel. To work as a precise macro calculator, this tool applies a strategy called Calorie Cycling:

• Training Days: You eat at Maintenance or a tiny surplus (+5%). The extra carbs fuel those heavy lifts and help you recover.
• Rest Days: You eat in a Moderate Deficit (-10% to -20%). Lower carbs keep insulin low and encourage your body to tap into fat stores for energy.

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Ready to Get your Baseline Scan? Book your BodySpec DEXA Here!

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The Science: Why "Recomp" Works

Why Not Just Starve the Fat Away?

Aggressive diets don't work for building muscle because creating new tissue is energy-expensive. If you cut calories too drastically, your body undergoes metabolic adaptation (often mislabeled as "survival mode"). It prioritizes essential functions and deprioritizes expensive processes like muscle growth to strictly conserve energy. Recomp finds the sweet spot: feeding you enough to build, but just slightly less than you need to maintain fat stores.

Protein is Non-Negotiable

Research consistently shows that recomposition requires high protein intake—often higher than standard recommendations.

• The Target: 1.0g to 1.2g per pound of Lean Body Mass (not total weight).
• Why? In a calorie deficit, your body might try to break down muscle for fuel. High protein intake stimulates muscle protein synthesis, effectively signaling your body to preserve lean mass (Jäger et al., 2017).
• Deep Dive: Check out How Much Protein to Prevent Muscle Loss for a detailed breakdown.

The "Wild Cards": Genetics, Hormones, and NEAT

Calculators give you a great starting point, but they can't see your DNA. Your actual daily burn is influenced by three major factors:

1. Genetics & Hormones: Some people naturally burn energy faster or partition nutrients better due to genetic variations in hormone signaling, such as insulin or thyroid pathways (Barzilai et al., 2010).
2. NEAT (Non-Exercise Activity Thermogenesis): This is the energy you burn doing everything that isn't sleeping, eating, or dedicated exercise—fidgeting, walking to the car, typing, or standing while you talk. Believe it or not, high NEAT levels can burn hundreds of extra calories a day and vary widely between individuals (Levine, 2002).
3. Sleep: Poor sleep elevates cortisol, which fights against muscle growth and promotes fat retention (Dattilo et al., 2011). (See also: Sleep Optimization Techniques).

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FAQ: Troubleshooting Your Recomp

Can I do this forever?

Not really. Recomposition gets harder the leaner you get. Beginners (or "newbies") can see amazing results for 6–12 months. Eventually, as you get closer to your genetic potential, you may need to switch to dedicated "bulking" or "cutting" phases to see changes.

The scale isn't moving. Is it broken?

Ignore the scale; watch your performance and the mirror.

• Good Sign: Your gym weights are going up, but your pants feel looser.
• Bad Sign: You feel weak or constantly burnt out, and your waist measurement isn't budging despite your efforts (this can sign you're undereating or overtraining).

How accurate is this number?

Think of it as an educated guess. Use these numbers for 4 weeks and monitor your results.

• Losing weight too fast? Add 150 calories to your training days.
• Gaining fat or looking puffy? Drop your rest day calories by 150.

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Verify Your Progress

The only way to truly know if you’re pulling off a successful recomp is to look under the hood. A bathroom scale can’t tell the difference between water, muscle, and bone.

Book a BodySpec DEXA Scan Near You
Get your precise Lean Mass number to plug into the Katch-McArdle calculator above, and re-scan in 8–12 weeks to see exactly how many pounds of muscle you’ve built.