If you are comparing Katch-McArdle vs Mifflin-St Jeor, the short answer is this: Mifflin-St Jeor is usually better for the general population, while Katch-McArdle is often better when you know your body fat percentage and want a lean-mass-based estimate. If you already have body composition data, try the Katch-McArdle BMR Calculator. If you do not, a standard TDEE Calculator based on Mifflin-St Jeor is usually the smarter default.
The reason this matters is simple: your calorie plan is only as useful as its baseline. If your BMR estimate is badly off, your maintenance, surplus, and deficit numbers all drift with it.
This guide explains how both formulas work, where each shines, and how lifters should choose between them in real-world nutrition planning.
■First: BMR vs TDEE
Before comparing formulas, separate these two ideas:
- ■BMR is how many calories your body burns at complete rest.
- ■TDEE is your total daily energy expenditure after activity is added.
Both Katch-McArdle and Mifflin-St Jeor estimate BMR, not full TDEE.
Once you have BMR, you multiply by an activity factor to estimate TDEE. That TDEE is what you actually use to set:
- ■maintenance calories
- ■calorie deficits
- ■calorie surpluses
■The Mifflin-St Jeor Formula
Mifflin-St Jeor estimates BMR from:
- ■total body weight
- ■height
- ■age
- ■sex
The formulas are:
Men
BMR = (10 x weight in kg) + (6.25 x height in cm) - (5 x age) + 5
Women
BMR = (10 x weight in kg) + (6.25 x height in cm) - (5 x age) - 161
This formula works well for the general population because it does not require body fat data. That is a big advantage. Most people do not know their body fat percentage with enough accuracy to improve on it.
■The Katch-McArdle Formula
Katch-McArdle uses lean body mass instead of total body weight.
BMR = 370 + (21.6 x lean body mass in kg)
To use it, you first need lean body mass:
lean body mass = total weight x (1 - body fat percentage)
That makes the logic very different from Mifflin-St Jeor. Katch-McArdle does not care about age, height, or sex directly. It assumes that metabolically active tissue is what matters most, and lean mass is its shortcut for that.
■Why Katch-McArdle Can Be Better for Lifters
Two people can weigh the same and have very different body composition.
Example:
- ■Person A: 180 lbs at 12 percent body fat
- ■Person B: 180 lbs at 30 percent body fat
They have the same scale weight, but not the same lean mass. The more muscular person generally burns more calories at rest.
That is exactly the kind of situation where Katch-McArdle shines. It accounts for differences in body composition directly instead of assuming average composition.
This is especially helpful for:
- ■lean strength athletes
- ■bodybuilders
- ■muscular trainees
- ■people using DEXA or reliable body fat measurements
If you already track body composition with the FFMI Calculator, Katch-McArdle often gives you a more personalized calorie baseline than a general-population formula.
■Why Mifflin-St Jeor Is Still the Better Default for Many People
The catch is body fat accuracy.
Katch-McArdle is only better if your body fat estimate is good enough to justify using it. If your body fat guess is poor, the formula can become less accurate than Mifflin-St Jeor.
That is why Mifflin-St Jeor remains the best default for many people:
- ■it needs only data most people know
- ■it performs well across the general population
- ■it avoids the biggest source of user error: bad body fat estimates
So the real choice is not just "which formula is theoretically better?" It is:
Which formula is better with the quality of data I actually have?
■Side-by-Side Example
Let us compare both formulas for the same lifter.
Example lifter
- ■body weight: 190 lbs (86.2 kg)
- ■height: 5'11" (180 cm)
- ■age: 32
- ■sex: male
- ■body fat: 15 percent
Mifflin-St Jeor
BMR = (10 x 86.2) + (6.25 x 180) - (5 x 32) + 5
BMR = 862 + 1125 - 160 + 5
BMR = 1832 calories
Katch-McArdle
First calculate lean body mass:
86.2 x (1 - 0.15) = 73.3 kg
Then:
BMR = 370 + (21.6 x 73.3)
BMR = 370 + 1583
BMR = 1953 calories
That is a difference of about 121 calories per day at the BMR level before activity is even applied.
Once you convert both to TDEE, the gap gets larger.
■When the Difference Matters
A 100 to 200 calorie daily difference is not trivial.
That can be the difference between:
- ■maintaining weight vs slowly gaining
- ■losing 0.5 lb per week vs barely moving
- ■feeling well fueled vs oddly flat in the gym
This is why formula selection matters most when:
- ■you are already relatively lean
- ■you are highly muscular
- ■you are deep into a cut
- ■you want tighter macro planning
For a casual trainee, the difference may not matter much. For someone trying to preserve performance and body composition, it can.
■Which Formula Should You Use?
Here is the most practical rule set.
Use Mifflin-St Jeor if:
- ■you do not know your body fat percentage
- ■your body fat estimate is a guess
- ■you want a dependable general baseline
- ■you are close to average body composition
Use Katch-McArdle if:
- ■you know your body fat percentage reasonably well
- ■you are unusually lean or muscular
- ■you want a lean-mass-based estimate
- ■you are tracking physique and calories closely
That is why many lifters use both:
- ■Mifflin-St Jeor as a general check
- ■Katch-McArdle as the more individualized estimate
Then they compare the result against real-world trend data like weekly scale change, gym performance, and hunger.
■The Formula Is Only the Starting Point
This is the part most people miss.
No formula, no matter how elegant, knows:
- ■your non-exercise movement
- ■your stress levels
- ■your sleep quality
- ■how much you fidget
- ■how hard your actual training feels
So even the "better" formula is still just a starting estimate.
The real process looks like this:
- ■Choose the best formula for your data quality.
- ■Estimate BMR and TDEE.
- ■Set calories for the goal.
- ■Track body weight and performance for 2 to 3 weeks.
- ■Adjust based on actual results.
If fat loss is your goal, How to Calculate Your TDEE for Weight Loss (Without Losing Strength) covers that adjustment process in more detail.
■Common Mistakes
Treating Formula Output as Exact
It is an estimate, not a metabolic lab result.
Using Katch-McArdle With a Bad Body Fat Guess
That removes the very advantage the formula is supposed to provide.
Ignoring Performance
If your calories say "maintenance" but your strength is dropping and recovery is awful, the formula does not get the final word. Your actual training response does.
Never Recalculating
As body weight and body composition change, calorie needs change too.
■A Good Practical Strategy for Lifters
If you want the simplest decision tree:
- ■Use Mifflin-St Jeor if your body fat data is weak.
- ■Use Katch-McArdle if your body fat data is strong.
- ■Compare the result to real-world trend data for 2 to 3 weeks.
That gives you both a rational starting point and a built-in correction mechanism.
■FAQ
Is Katch-McArdle more accurate than Mifflin-St Jeor?
It can be, especially for lean or muscular people who know their body fat percentage reasonably well. Without good body fat data, Mifflin-St Jeor is often the better choice.
Which formula is best for bodybuilders or muscular lifters?
Katch-McArdle is often more useful because it accounts for lean mass directly.
Which formula is best if I do not know my body fat percentage?
Mifflin-St Jeor. It requires only weight, height, age, and sex.
Should I use both formulas?
You can. Many lifters use both as a range, then refine the target based on scale trends and gym performance.
What tool should I use first?
Start with the Katch-McArdle BMR Calculator if you know body fat, or the TDEE Calculator if you want the simplest baseline.