Most men can naturally gain 40-to-50 pounds of muscle in their lifetimes, and most women can naturally gain 20-to-25 pounds. But how much can you gain, exactly?

Research conducted by scientist and natural bodybuilder Casey Butt shows that your bone structure can help predict your lifetime muscle gain potential.

Enter your height, estimated body fat percentage, and wrist and ankle circumferences into the maximum muscle potential calculator below to estimate how “jacked” you can get without steroids.

How to Use the Muscle Gain Calculator

Our muscle gain calculator is designed to be user-friendly and accurate, and to offer insights into your potential for muscle growth based on well-established scientific research.

Here’s how to calculate your muscle potential using the muscle potential calculator devised by Casey Butt:

  1. Choose your preferred measurement unit (imperial or metric).
  2. Enter your height.
  3. Enter your wrist circumference. To measure, find the bony lump on the outside of your wrist (the styloid process), open your hand, and wrap a tape measure around the space between that lump and your hand.
  4. Enter your ankle circumference. To measure, wrap a tape measure around your lower leg between your ankle bone and your calf muscle. Move the tape measure around to find the narrowest point.
  5. Enter your ideal body fat percentage if you were to be at 100% of your muscle-building potential. I recommend 10% because lower than that isn’t sustainable for most guys.

You may have noticed that our muscle potential calculator gives you two results: your maximum potential for muscle gain and your realistic potential for muscle gain.

The reason for this is that although Butt based the formulas on records from “natural bodybuilders,” many of these competitors may have been using drugs. It’s easy to cheat drug tests in most sports—bodybuilding especially—and steroids were legal and generally not tested for until about the 1980s.

Thus, it’s safe to assume that undisclosed steroid use may have slightly inflated Butt’s numbers. Additionally, much of the data came from top-level bodybuilders who comprise the genetic elite for muscle gain.

Therefore, it’s wise to look at your maximum numbers from the calculator as an absolute ceiling of what you could achieve if you did everything right with your training and nutrition for years.

And it’s reasonable to subtract 5% from your maximum drug-free results for a more conservative estimate of how big we can get without more or less devoting our lives to lifting weights.

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Timeline for Reaching Your Natural Genetic Potential

It takes at least 4-to-5 years of proper dieting and training to approach your genetic potential for muscle growth. After this point, further gains in muscle mass become vanishingly small.

However, the time it takes to reach your genetic potential can vary depending on numerous factors.

For example, the quality and consistency of your diet and training can accelerate or delay your progress. Many people spin their wheels with suboptimal training programs (or worse, just “exercise”) and make various mistakes in the kitchen (like not eating enough calories or protein), which prevent them from making progress as quickly as they should.

Could The Muscle Gain Calculator’s Results Be Wrong?

The maximum muscle potential calculator gives you an insight into the highest muscle mass you could achieve naturally, based on the strongest evidence we have.

That said, you may not like the results the genetic potential calculator gives you, leading you to doubt its accuracy.

While there’s a slight chance the muscle gain calculator is wrong, it’s more likely that you have unrealistic expectations of how much muscle you can build naturally.

Chances are you follow several bodybuilders, fitness models, and influencers who might make your muscle gain potential seem modest. And that’s okay. 

In fact, it’s good you’re realizing this now before unrealistic hopes can sink their hooks in and set you up for major disappointment and failure later (or worse, steroid use).

However, the good news is, irrespective of your genetic potential or perceived “genetic limiters,” you can still build an outstanding physique.

If a guy new to weightlifting gains 30-to-40 pounds of muscle and stays around 10% body fat, he’ll look like a Greek god to most people. Similarly, as a woman, you’ll likely love how you look after adding just 10-to-15 pounds of muscle in the right places and dieting down to about 20% body fat.

The journey to your dream physique might take longer than anticipated, and you may never be as muscular or defined as your Instagram idols. Still, you absolutely can transform your physique into something special.

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How Can You Tell if Someone Is Taking Steroids?

In some cases, it’s easy to tell if someone’s on steroids.

For example, if they’re an IFBB pro or resemble one, they’re using steroids.

It’s rarely that obvious, though. Most steroid users don’t look like professional bodybuilders or physique athletes. In fact, many look far more “ordinary” than you might think.

In these cases, calculating their fat-free mass index (FFMI), which measures muscle mass relative to height, is the most reliable way to determine if they’re using or have used steroids.

You can do this for yourself by dividing your lean body mass in kilograms by your height in meters squared. Alternatively, use the Legion FFMI Calculator to do the number crunching for you.

How to Build Muscle Naturally

As you begin your fitness journey, having clear goals and a solid plan are crucial.

To plan effectively, use the muscle gain calculator to understand your muscle-building potential. This tool helps you understand the amount of muscle you can gain naturally, allowing you to set realistic and achievable goals.

With this knowledge in hand, here’s everything you need to know about gaining muscle naturally:

1. Eat the right number of daily calories.

The primary concern for most dieters is weight loss. The only way to drive fat loss and lose weight is to eat fewer calories than you burn.

This is the opposite of what you want to do when gaining muscle. 

Research shows that the sweet spot for maximizing muscle gain while minimizing excess weight gain is somewhere around 110% of your TDEE (the number of calories you burn each day based on your body weight, height, age, and activity level).

Thus, calibrate your daily caloric intake to maintain a daily calorie surplus of about 10%.

2. Learn to track macros.

In addition to eating the right number of calories, consuming enough protein to build and repair muscle is crucial.

A good guideline to maximize muscle growth is to eat 0.8-to-1 gram of protein per pound of body weight per day.

To learn more about tracking macros, check out the Legion Macro Calculator. Or, for even more in-depth advice about nutrition, take the Legion Diet Quiz.

3. Prioritize heavy weightlifting.

To provide your muscles with a powerful muscle-building stimulus, dedicate most of your training time to compound exercises.

These exercises train the most full-body muscle, allow you to lift heavy weights safely, and progress regularly, making them ideal for gaining muscle and strength.

If you want a strength training program that includes all the best muscle-building exercises, check out my fitness books for men and women, Bigger Leaner Stronger or Thinner Leaner Stronger.

FAQ #1: How many calories do I need to gain muscle but not fat?

Research shows that the sweet spot for maximizing muscle gain while minimizing fat gain is somewhere around 110% of your total daily energy expenditure. 

Thus, to maximize muscle gain while minimizing fat gain, maintain a calorie surplus of about 10%. For most people, this comes out to 16-to-18 calories per pound of body weight per day, depending on how physically active you are.

For an exact calorie target based on your body and activity levels, check out the Legion Calorie Calculator.

FAQ #2: What macros are needed for muscle gain?

To maximize muscle building while you lean gain, follow these recommendations:

  • Consume 0.8-to-1 gram of protein per pound of body weight per day.
  • Consume 30-to-50% of your daily calories from carbohydrate, which comes out to about 0.75-to-2 grams of carbs per pound of body weight per day for most people.
  • Consume 20-to-30% of daily calories from fat, which is 0.2-to-0.4 grams of fat per pound of body weight per day for most people.

FAQ #3: How long can I continue to build muscle?

If you’re diligent with your workout and diet routines, you can expect to continue gaining muscle for about 4-to-5 years. After this, muscle growth slows down significantly.

There’s some debate among scientists about whether muscle gain completely stops or just becomes minuscule, but practically speaking, continuous, substantial muscle and strength gains are not feasible indefinitely without resorting to steroids.