Body Recomposition Calculator

This body recomposition calculator works out what to eat to lose fat and build muscle at the same time, then tells you how long it will take to reach the body fat you are aiming for. It runs the 2023 NASEM energy equations, and it holds your deficit under the line where a meta-regression found that gains in lean mass stop: about 500 calories a day.

What This Body Recomposition Calculator Needs From You

Four numbers and three dropdowns.

1. Tell it how you know your body fat. Got a reading from a DXA scan, an InBody or another scale? Enter it. No number? Pick the waist-only tape (weight plus your waist at the navel) or the neck-and-waist Navy method (neck and waist, plus hips for women).
2. Enter your sex, age, height, weight and goal body fat. Imperial is the default. Tap Metric for centimeters and kilograms.
3. Set your focus, your lifting history, your training days and your activity level. Focus is the important one: balanced, lean out first, or build muscle first.
4. Hit Calculate. You get your daily calories, a protein, carb and fat split, your lean and fat mass in pounds, the months to your goal, a 12-week projection, and a waist-to-height health check.

About that activity dropdown. It changes your answer more than anything else on the page, so the options use NASEM's own descriptions rather than gym-speak. Low active is the default because it fits most people who lift a few times a week and sit down for work. Pick Active only if you really do move for about two hours a day.

What the Research Actually Says About Recomposition

Here is the finding that should shape your expectations, and almost nobody quotes it.

A 2022 meta-analysis pooled every randomized trial of at least three weeks where people lifted weights in a calorie deficit. Lean mass gains were clearly worse in a deficit than in a control group eating at maintenance (effect size −0.57, p = 0.02). Strength gains were not (−0.31, p = 0.28). The meta-regression then put a number on it: a deficit of about 500 calories a day prevented gains in lean mass altogether.

Two things follow from that, and they are the honest version of every recomp promise you have read:

• Your lifts will keep going up even when your muscle is not. So the bar getting heavier is not proof the recomp half is working. That is the single most common way people fool themselves.
• The deficit is a dial, not a switch. Every calorie you take out speeds up fat loss and slows down muscle gain. This calculator scales your expected muscle gain down as your deficit grows, rather than promising both at full speed.

Higher body fat and less training history are what tip the odds in your favor, which is why the calculator rates your potential from your body fat, your age and how long you have been lifting. If you are already lean and experienced, it will tell you that separate phases will probably serve you better. That is not the answer most tools give, and it is the true one.

Where Your Maintenance Calories Come From

Almost every recomposition calculator online starts with the Mifflin-St Jeor equation from 1990, works out your resting metabolic rate, then multiplies it by an activity factor. This one does not. It uses the 2023 NASEM total energy expenditure equations, built on doubly labeled water measurements, which estimate what you actually burn in a day in one step instead of guessing a multiplier.

You can check that it is implemented correctly, which is not something you can usually do with a calculator. The NASEM report publishes its own worked example: the average adult man in its database, 50.3 years old, 175.9 cm and 83.1 kg at an active level, should come out at 2,930 calories. Enter him here and this calculator returns 2,929. The average woman, 53.9 years, 162.3 cm, 71.9 kg, should be 2,281. It returns 2,281.

Activity level is where most of the movement is. Same man, 28 years old, 5'10", 190 pounds, only the dropdown changed:

That is a 780 calorie spread from one dropdown, which is why the labels are worth reading twice.

The Error Bar Is Bigger Than the Deficit

Now the part no other recomposition calculator will tell you, and the reason this page exists.

NASEM publishes the uncertainty on its own equations. For adults, the standard error of the predicted value is 342 calories for men and 241 for women. Run the 95% interval on our example man and his true maintenance sits somewhere between 2,370 and 3,710 calories.

Read that next to his prescription. A balanced recomp puts him 10% below maintenance, which is 304 calories.

His deficit is smaller than the error bar on the number it was subtracted from. That is not a flaw in this calculator; it is true of every calorie calculator ever built, and the others simply do not mention it. It has one practical consequence, and it is the most useful thing on this page:

The calorie number is a starting point, not a measurement. Hold it for two to four weeks, weigh yourself the same way each morning, take a waist measurement, and let the trend tell you whether the estimate was high or low. Then move by 100 to 200 calories. The scale and the tape measure are data. The calorie estimate is a hypothesis.

How Big Should Your Deficit Be?

The three focus settings all resolve to a deficit, and here is exactly what each one does, because the trade-off is not obvious:

• Balanced takes 10% of your maintenance. For our man, 304 calories.
• Lean out first takes 20% of maintenance, capped at 500 calories a day so you stay under the research ceiling, and never below 420, which is the deficit that produces a pound of fat loss every ten days. For a big man the cap bites and he gets 15%. For a smaller woman the floor lifts her to 23% or more.
• Build muscle first takes nothing off. You eat at maintenance, muscle comes on fastest, and fat comes off slowly or not at all.

What those numbers buy, for a 190 pound man at 24% body fat who is new to lifting:

Notice the row where the scale barely moves. That is textbook recomposition, and it is also the row where you will be most tempted to quit, because nothing appears to be happening. Take a photograph instead.

A Worked Example, Start to Finish

A man, 28, 5'10", 190 pounds, 24% body fat, aiming for 15%. Balanced focus, new to lifting, three lifting days, low active.

• Maintenance: 3,040 calories (NASEM 2023)
• Deficit: 304 calories, so eat 2,740
• Macros: 155 g protein, 359 g carbs, 76 g fat
• Body composition now: 144.4 lb lean, 45.6 lb fat
• Pace: 2.3 lb of fat and 0.7 lb of muscle a month, so the scale drops about 0.4 lb a week
• Time to 15%: 8 months, finishing near 177 pounds
• After 12 weeks: 185.6 lb on the scale, 146.4 lb lean, 39.2 lb fat, 21.1% body fat

Look at the 12-week line. He loses 6.4 pounds of fat and gains 2.0 pounds of muscle, but the scale only shows 4.4 pounds gone. Anyone judging that by body weight alone would conclude it half worked.

Protein is the number to defend when calories come down, which is why it is set from your goal weight rather than your current weight. Our protein calculator works it out on its own if you want a second opinion.

The Waist Check Most Calorie Tools Skip

Enter a waist measurement and the calculator runs a second check that has nothing to do with calories. It divides your waist at the navel by your height, the measure the UK's health guideline body now recommends alongside BMI. The body roundness index calculator reads those same two numbers against bands set by age and sex, rather than one cutoff for everyone.

The rule is easy to remember: keep your waist under half your height. At 5'10" that means under 35.0 inches. NICE sorts the result into three bands, 0.4 to 0.49 as healthy, 0.5 to 0.59 as increased risk, and 0.6 or more as high risk.

Here is the part almost every site quoting those bands leaves out. NICE applies them only below a BMI of 35. Above that, waist-to-height stops being the right instrument and the guideline sends you to BMI class instead. So if your BMI is 35 or higher, this calculator shows your ratio but withholds a risk label it cannot support. Most tools print it anyway.

Why this belongs on a recomposition page: the scale is the one number a successful recomp will not move. Your waist is. Measuring it at the same spot every four weeks is the cheapest progress check you have, and it doubles as the health check.

The second row uses the American Council on Exercise body fat categories, which put 18 to 24% in the average band for men and 25 to 31% for women. Those are fitness-industry bands rather than clinical ones, and the calculator labels them as ACE's for that reason.

How Four Popular Tools Answer the Same Question

We put the same man through every working recomposition calculator on page one of U.S. Google results on September 23, 2026.

A 450 calorie spread in what he is told to eat, and four different answers about protein. None are arithmetic mistakes; they are different equations and different assumptions, all defensible. What none of them will do is ask what body fat you are aiming for, which is why none can answer the question people actually arrive with.

What This Calculator Cannot Tell You

• It cannot measure you. Every output rests on your body fat number, and a tape estimate typically misses a DXA reading by about 4 points in men and 4 to 5 in women.
• Muscle-gain rates are practical estimates from training experience, not measurements of you.
• It assumes hard, progressive resistance training, enough sleep and reasonable adherence. Remove any of those and the muscle half stops first.
• It will not tell you whether your goal body fat is a good goal. Very low targets carry their own costs, and if you picked yours because you want visible abs, the number you actually need is not the number most pages quote.
• It measures speed, not standing. To see how much muscle you already carry for your height, use our FFMI calculator instead.

This calculator is for informational and screening purposes only and does not constitute medical advice or diagnosis. Always consult a qualified healthcare professional.

Frequently Asked Questions