Katch-McArdle calculator (BMR and TDEE from body fat %)
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Your likely daily energy use
2,143 as low as
2,408 kcal/day
2,673 as high as
±11% — the shaded band is where your real figure most likely sits.
Show the arithmetic
- Lean body mass
- 82 kg × (1 − 22%) = 64 kg
- BMR (Katch-McArdle)
- 370 + 21.6 × 64 = 1752 kcal
- Activity — Lightly active
- 1752 × 1.375 = 2408 kcal
- Honest band — ±11%
- 2143 – 2673 kcal/day
Mifflin-St Jeor is the default because it is the best-validated equation that needs no body-fat number. Harris-Benedict would give 1,848 kcal for the same person — a difference of well under 100 kcal. The formula is not what makes these calculators wrong; the activity multiplier is.
Where your calories go
Estimated daily breakdown of your 2,408 kcal TDEE.
- BMR (Resting) 1,752 kcal (73%)
Organs, brain & heart function at complete rest
- TEF (Food digestion) 241 kcal (10%)
Energy spent digesting protein, carbs & fats (~10%)
- NEAT (Daily movement) 291 kcal (12%)
Walking, standing, fidgeting & non-exercise movement
- EAT (Workouts) 125 kcal (5%)
Structured workouts, sports & cardio sessions
So what do I eat?
One recommendation, not a menu. Moderate loss is marked because it is the rate most people actually sustain. Pick another row to move the numbers.
1,927 kcal/day · -0.44 kg per week, estimated
Macros — as ranges, because that is what the evidence supports
- Protein 148–180 g 1.6–2.2 g per kg bodyweight, upper end while cutting
- Fat 43–64 g 20–30% of calories
- Carbs 157–238 g whatever the calorie target has left
How to replace this estimate with your own number
Every figure on this page is a starting point, and the ±band is the honest size of the error. After two to three weeks of eating near your target, weigh yourself daily and compare the weekly averages, not single days. If the average moved less than the estimate predicted, your real maintenance is lower than shown — subtract roughly 100 kcal and hold for another fortnight. If it moved faster, add 100. Two cycles of that beat any formula, including this one.
2–3 Week Self-Correction Calculator
Calculators estimate; your body provides ground truth. Enter your 2–3 week progress to calculate your actual real-world TDEE.
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What the Katch-McArdle calculator does
Most BMR calculators, including the default on the homepage, estimate your resting metabolism from your weight, height, age and sex. The Katch-McArdle equation does something different: it works only from your lean body mass: everything you are made of except fat. Enter a body-fat percentage above and this calculator switches to it automatically.
The logic is sound. Fat tissue is close to metabolically inert; muscle, organs and bone are what actually burn calories at rest. Two people at the same weight but different body compositions have genuinely different resting rates, and an equation built on total weight cannot see that. Katch-McArdle can.
The catch is in the input. Katch-McArdle is only as good as the body-fat number you feed it, and a bad estimate makes it worse than the equation it replaced.
The Katch-McArdle formula
It is one of the simplest equations in the field:
BMR = 370 + 21.6 × LBM(kg)LBM (lean body mass) = weight × (1 − body-fat%). No age term, no sex term.
So a 75 kg person at 18% body fat has a lean mass of 61.5 kg and a Katch-McArdle BMR of about 1,699 kcal. The same equation, published by Katch and McArdle in Exercise Physiology, is numerically identical to the revised Cunningham equation: the two names describe the same line.
Because there is no age or sex correction, the whole estimate rests on getting lean mass right, which means getting body fat right.
When Katch-McArdle beats Mifflin-St Jeor, and when it is worse
Katch-McArdle is the better choice when both of these are true:
- Your body composition is away from the average the weight-based equations assume: you are lean and muscular, carrying more or less muscle than typical, or heavy in a way that is mostly muscle.
- You have a measured body-fat percentage, not a guess.
If you do not have a real measurement, use the Mifflin-St Jeor calculator. It is the most reliable equation for the general population in the published comparisons, and it needs nothing you have to estimate. Feeding Katch-McArdle a guessed body-fat number ("I look about 15%") typically introduces more error than it removes, while the lean-mass framing makes the result feel more precise. That false confidence is the trap. How accurate is a TDEE calculator covers this in more depth.
Getting a body-fat number you can trust
Ranked roughly by how much you can rely on the figure:
- DEXA scan: the practical reference standard. A single scan is enough to run this equation for months.
- Hydrostatic weighing or a BodPod: accurate, less widely available.
- Skinfold calipers: good in a trained hand, using a multi-site formula. Poor when self-administered on the first attempt.
- Bioelectrical impedance (smart scales, handheld devices): swings several points with hydration, time of day and recent food. Fine for tracking a trend, weak as an absolute number for an equation.
- Visual estimation from photos: better than a pure guess, still a wide margin. Use it only if you have nothing else, and expect the estimate to be soft.
If your only figure comes from a BIA scale, it is reasonable to run both equations and treat the gap between them as part of the uncertainty band rather than trusting either to the calorie.
From BMR to TDEE and macros
The Katch-McArdle number is your BMR: the resting figure. To get your TDEE, this tool multiplies it by the same activity factor (1.2 to 1.9) as every other formula here; the difference between BMR and TDEE is entirely that step. From there, the goal shift and the protein, fat and carbohydrate split work exactly as on the macro calculator; Katch-McArdle only changes how the starting BMR was estimated, nothing downstream.
What this calculator cannot tell you
It cannot verify your body-fat percentage, and it inherits every limitation of the number you enter. Lean mass itself varies in metabolic activity between people, so even a perfect body-fat reading leaves a residual error the equation cannot close. And like every prediction here, it is a starting point to replace with two to three weeks of your own weight data.
This page is written by Madhu Kinnera, who is not a clinician. Nothing here is medical advice. The equation and the accuracy comparisons above come from the primary literature: Cunningham (1991) for the lean-mass equation itself, and Frankenfield et al. (2005) for Mifflin-St Jeor being the most reliable general-population equation. If you are pregnant, have a condition affecting your metabolism, or are planning a large change in intake, speak to a doctor or a registered dietitian first.
Frequently asked questions
What is the Katch-McArdle formula?
BMR = 370 + 21.6 × lean body mass in kilograms, where lean body mass is your weight multiplied by (1 minus your body-fat fraction). It has no age or sex term: the entire estimate comes from how much lean tissue you carry. It is numerically the same as the revised Cunningham equation.
Is Katch-McArdle more accurate than Mifflin-St Jeor?
Only when you have a measured body-fat percentage and a body composition away from average: lean, muscular, or unusually heavy with muscle. With a guessed body-fat number it is usually less accurate than Mifflin-St Jeor, which is the most reliable equation for the general population and needs no estimated input.
Do I need to know my body fat percentage to use it?
Yes, it is the only input that matters beyond your weight. Without a real measurement (DEXA, hydrostatic, BodPod, or skilled calipers), use the Mifflin-St Jeor equation instead. A guessed body-fat figure makes the Katch-McArdle result look precise while making it less correct.
How do I calculate my lean body mass?
Multiply your body weight by (1 minus your body-fat percentage expressed as a decimal). At 80 kg and 20% body fat, lean body mass is 80 × 0.80 = 64 kg. That figure is what goes into the Katch-McArdle equation.
Is Katch-McArdle good for building muscle or bulking?
It is well suited to lifters because it responds to the muscle you have rather than assuming an average. As you gain lean mass and re-measure your body fat, your estimated BMR rises accordingly. Pair the result with a surplus of roughly 10% over TDEE and a protein target of 1.6–2.2 g/kg.
Why does Katch-McArdle ignore age and sex?
Because it assumes those factors act on metabolism mainly through body composition, which it already measures directly. A 25-year-old man and a 55-year-old woman with the same lean mass get the same estimate. That is a strength when body fat is measured and a weakness when it is guessed.
What is the difference between Katch-McArdle and Cunningham?
In practice, none. The Katch-McArdle equation used here (370 + 21.6 × lean mass) is identical to the revised Cunningham equation. Cunningham\u2019s original 1980 version used slightly different constants and produces a marginally higher figure.
Can I use a smart scale body-fat reading with this calculator?
You can, but treat it cautiously. Bioelectrical impedance readings shift by several percentage points with hydration and time of day, and a few points of body fat moves the BMR estimate noticeably. Running both Katch-McArdle and Mifflin-St Jeor and taking the range between them is a reasonable hedge.
Does the Katch-McArdle calculator give me my TDEE too?
Yes. It estimates your BMR from lean mass, then multiplies by an activity factor between 1.2 and 1.9 to produce your TDEE, and splits that into macros for your goal. The lean-mass method only changes the first step; everything after it is the same as the other calculators here.
Is Katch-McArdle accurate for people with obesity?
Less so. The equation was derived largely in lean and athletic populations, and at higher body-fat levels the relationship between lean mass and resting rate is weaker. For higher body-fat ranges, Mifflin-St Jeor tends to perform at least as well and needs no body-fat input.
What activity multiplier should I use with Katch-McArdle?
The same ones as any TDEE calculation: 1.2 sedentary, 1.375 lightly active, 1.55 moderately active, 1.725 very active, 1.9 extremely active. Most people should pick a lower bucket than they expect: the multiplier is the input most likely to be wrong, whichever BMR equation feeds it.
How often should I re-run it?
Whenever you have a fresh body-fat measurement, and after every 5–10 kg of weight change. Between measurements, your own weekly weight trend is a better guide than re-running any equation: the formula cannot see the adaptation your scale already recorded.
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