When you search for a calorie calculator, you will see three names come up again and again — BMR, TDEE, and the Mifflin-St Jeor formula. Most people think these are three different tools doing the same job. They are not. Each one plays a specific role in figuring out how many calories your body actually needs. Use the wrong one and your calorie target will be off from day one.
The Mifflin-St Jeor formula is considered the most accurate BMR and TDEE calculator for most people. But understanding why — and when the other formulas work better — is what this guide covers clearly.
| Formula | Best For | Accuracy |
|---|---|---|
| Mifflin-St Jeor | Most people | Best overall |
| Harris-Benedict | General use | Good but older |
| Katch-McArdle | Athletes with known body fat % | Most accurate when lean mass is known |
Key Takeaways
- Mifflin-St Jeor is the best formula for most people
- Harris-Benedict is older and slightly less accurate
- Katch-McArdle is best if you know your body fat percentage
- Your TDEE depends on both your BMR and your activity level
- Real-world tracking matters more than any perfect formula
Why There Are Different TDEE Formulas
Different research teams developed these formulas at different times, using different groups of people. Each formula uses a slightly different calculation method, which means they can produce different BMR results for the same person.
The formula you choose affects your BMR number. Your BMR number affects your TDEE. And your TDEE is the calorie target everything else is built on. So it is worth taking two minutes to understand which one fits your situation.
Why BMR Is Calculated Before TDEE
Every TDEE calculation starts with BMR. Once your BMR is estimated, it is multiplied by an activity factor to estimate your total daily calorie needs.
BMR stands for Basal Metabolic Rate. It is the number of calories your body burns at complete rest — just to keep your heart beating, lungs working, and organs functioning. It is the floor, not the ceiling.
TDEE — Total Daily Energy Expenditure — is your BMR multiplied by how active you are. It represents every calorie your body burns across a full day, including movement, exercise, and digestion.
Get your BMR formula right, then apply the correct activity multiplier, and you have a reliable TDEE to work from.
How BMR, TDEE, and the Three Formulas Work Together
Think of it this way:
- The formula (Mifflin-St Jeor, Harris-Benedict, or Katch-McArdle) is the method you use
- BMR is the result that formula produces
- TDEE is what you get when you multiply that BMR by your activity level
They are not competing options. They are connected steps. The formula choice only changes step one — but that step affects everything after it.
Which Formula Is Best for Most People?
Mifflin-St Jeor is the right starting point for most adults. It uses your weight, height, age, and sex — information almost everyone has — and it has been validated as the most accurate weight-based BMR formula across a broad range of body types.
Harris-Benedict works well too, but tends to overestimate slightly. Katch-McArdle is the most accurate option available — but only when you have a reliable body fat percentage measurement to work from.
Mifflin-St Jeor Formula — The Recommended Starting Point
The Mifflin-St Jeor formula was developed in 1990 and is recommended by the American Dietetic Association as the most accurate general-purpose BMR formula for the majority of adults.
Mifflin-St Jeor is considered the best general-purpose BMR formula because it performs consistently well across different ages, body weights, and body types. When registered dietitians and clinical nutritionists calculate a client’s calorie needs, this is typically the formula they use.
The Mifflin-St Jeor Formula for Men and Women
For Men:
BMR = (10 × weight in kg) + (6.25 × height in cm) − (5 × age in years) + 5
For Women:
BMR = (10 × weight in kg) + (6.25 × height in cm) − (5 × age in years) − 161
The only difference between the two is the final number — +5 for men, −161 for women. Everything else is identical.
What the Research Actually Shows
The Journal of the American Dietetic Association found Mifflin-St Jeor to be the most accurate BMR formula when tested against actual oxygen consumption in a clinical setting.
Key findings from the research:
- Accurate within 10% for 82% of people tested
- Outperformed Harris-Benedict in both accuracy and consistency
- Performed reliably across different age groups and body weights
- Recommended as the preferred formula for clinical and general use
Mifflin-St Jeor Is Best For
- Most adults — regardless of age or fitness level
- People focused on fat loss
- People focused on muscle gain
- General daily calorie tracking
- Anyone who does not know their body fat percentage
Worked Example — Mifflin-St Jeor in Action
Take Sarah — 30 years old, 65kg, 165cm tall, moderately active (gym 4 times per week).
Step 1 — Calculate BMR:
(10 × 65) + (6.25 × 165) − (5 × 30) − 161
= 650 + 1,031 − 150 − 161
= 1,370 kcal
Step 2 — Multiply by activity factor (×1.55 for moderately active):
1,370 × 1.55 = 2,124 kcal per day
Sarah’s TDEE is 2,124 calories. Eating at this level maintains her current weight. Eating 300–500 calories below it produces steady fat loss.
Harris-Benedict Formula — The Historical Standard
Harris-Benedict was the standard calorie formula for decades and is still widely used today. It was originally developed in 1919 and revised in 1984 to improve accuracy for modern populations.
If you have used a calorie calculator in the past and it did not ask for your body fat percentage, there is a good chance it was running Harris-Benedict in the background.
The Harris-Benedict Formula for Men and Women
For Men (Revised):
BMR = 88.362 + (13.397 × weight in kg) + (4.799 × height in cm) − (5.677 × age in years)
For Women (Revised):
BMR = 447.593 + (9.247 × weight in kg) + (3.098 × height in cm) − (4.330 × age in years)
Always use the revised version. The original 1919 formula overestimates BMR by 5–15% in modern populations. Most reputable calculators use the revised version automatically, but it is worth checking.
How Harris-Benedict Compares to Mifflin-St Jeor
Using the same person from the previous example — Sarah, 30, 65kg, 165cm:
- Mifflin-St Jeor result: 1,370 kcal
- Harris-Benedict result: approximately 1,412 kcal
- Difference: 42 calories per day
That 42-calorie gap feels small. But multiplied by an activity factor and used daily over weeks of dieting, it adds up. Over a month, that is roughly 1,260 extra calories — the equivalent of nearly two full days of unaccounted intake.
Harris-Benedict Is Best For
- General population use
- People who want a second formula to cross-check their Mifflin result
- Situations where Mifflin-St Jeor is not available in a tool
Where Harris-Benedict Falls Short
- Tends to overestimate BMR, especially in people with higher body fat
- Less accurate at the extremes — very lean athletes and significantly overweight individuals
- Based on older data that does not fully reflect modern body composition patterns
Katch-McArdle Formula — The Specialist Option
Katch-McArdle is the most accurate BMR formula available — but it requires one piece of information the other two do not: your lean body mass.
Lean body mass is your total weight minus your fat mass. To calculate it, you need to know your body fat percentage. This is why Katch-McArdle is not the default recommendation for most people — not because it performs poorly, but because most people do not have an accurate body fat measurement to work from.
The Katch-McArdle Formula
For All Genders:
BMR = 370 + (21.6 × lean body mass in kg)
No height, age, or sex required. The formula works entirely from lean mass because lean tissue — primarily muscle — is what drives calorie burn at rest.
How to Find Your Lean Body Mass
- DEXA scan — most accurate measurement available
- Hydrostatic weighing — highly accurate, less accessible
- Skinfold callipers — less precise but usable
- Body fat scales — convenient but variable accuracy
If you are estimating your body fat percentage without a proper measurement, the margin of error introduced into Katch-McArdle is large enough to make Mifflin-St Jeor the more reliable choice.
Worked Example — Katch-McArdle in Action
Using Sarah again — 65kg, and let us say her body fat is 28%.
- Fat mass: 65 × 0.28 = 18.2kg
- Lean body mass: 65 − 18.2 = 46.8kg
- BMR: 370 + (21.6 × 46.8) = 370 + 1,011 = 1,381 kcal
Compare that to Mifflin-St Jeor’s result of 1,370 kcal — just 11 calories apart for this individual. The two formulas converge closely for people with average body composition. They diverge more significantly for lean athletes or people with high body fat.
Katch-McArdle Is Best For
- Athletes and bodybuilders with known body fat percentage
- People who have had a DEXA scan or professional body composition assessment
- Lean individuals whose Mifflin-St Jeor result feels consistently low
Katch-McArdle becomes especially useful for lean athletes because muscle mass has a stronger effect on resting calorie burn than body weight alone. A very muscular person and a less muscular person of the same total weight will have very different BMRs — and only Katch-McArdle captures that difference directly.
BMR Formula Comparison — Mifflin-St Jeor vs Harris-Benedict vs Katch-McArdle
Here is a direct side-by-side comparison of all three formulas to help you choose the right one for your situation.
For most people, the difference between Mifflin-St Jeor and Harris-Benedict is 50–150 calories per day. For people at the extremes of body composition — very lean or very high body fat — the gap can reach 200–400 calories or more. That is a meaningful difference when you are managing a calorie deficit or surplus.
All three formulas give you a starting estimate. The most accurate TDEE you will ever have comes from tracking your food and weight together for 2–4 weeks and adjusting based on real results.
Which BMR Formula Should You Use?
Here is a simple decision based on your situation:
- You are an average adult without body fat data → Use Mifflin-St Jeor. It is the most validated general-purpose formula and the right default for most people.
- You are an athlete or bodybuilder with an accurate body fat measurement → Use Katch-McArdle. It accounts for lean mass directly and will give you a more personalised result.
- You want to cross-check your result → Run Harris-Benedict as well. If both results are within 100–150 calories of each other, start from the lower number to avoid overestimating your TDEE.
Whichever formula you use, treat the result as a starting point. Eat at your calculated TDEE for 2–3 weeks. If your weight stays the same, the number is accurate. If it changes, adjust by 100–200 calories in the appropriate direction and reassess.
Frequently Asked Questions
Is the Mifflin-St Jeor formula the most accurate?
For most people — yes. Research confirms it predicts resting energy expenditure more accurately than any other weight-based formula across a broad population. The only exception is people who know their precise lean body mass, for whom Katch-McArdle may be slightly more accurate.
What is the difference between Mifflin-St Jeor and Harris-Benedict?
Both use weight, height, age, and sex — but apply different calculations. Harris-Benedict was developed in 1919 and tends to overestimate BMR slightly. Mifflin-St Jeor was developed in 1990 using more modern data and corrects for that overestimation. For most people, the difference in daily BMR is between 50 and 150 calories.
Which BMR formula should I use for fat loss?
Use Mifflin-St Jeor unless you have an accurate body fat measurement. For fat loss, starting from a slightly conservative estimate and adjusting based on real results is safer than overestimating your TDEE from the beginning.
Does it matter which formula I use for my TDEE?
Yes — but not dramatically for most people. The formula affects your BMR, which affects your TDEE. A 100–200 calorie difference in your daily target compounds over weeks of dieting. Pick the most appropriate formula, track your weight for 2–3 weeks, and adjust based on what your results show.
What is a normal BMR for a woman?
Most adult women have a BMR between 1,200 and 1,600 calories per day. Shorter, lighter, or older women sit toward the lower end. Taller, heavier, or more muscular women sit higher. BMR alone is not a daily calorie target — multiply it by your activity level to get your TDEE.
What is a normal BMR for a man?
Most adult men have a BMR between 1,600 and 2,100 calories per day. Taller men with higher muscle mass tend to sit at the top of that range or above it. BMR alone is not a calorie target — always convert it to TDEE before using it to plan your intake.
Is Katch-McArdle better than Mifflin-St Jeor?
It can be — but only if your lean body mass is measured accurately. If you are estimating your body fat percentage, the error flows directly into your Katch-McArdle result. For athletes with a DEXA scan, Katch-McArdle is the stronger choice. For everyone else, Mifflin-St Jeor is more reliable and practical.