A century of service
James Harris and Francis Benedict published the original equation in 1919, derived from calorimetry measurements of 239 subjects — making it the formula that defined metabolic estimation for most of the 20th century.
Roza and Shizgal revised the coefficients in 1984 using a larger dataset, and it's the revised version that calculators (including ours) use today.
The revised formula
Men: BMR = 88.362 + 13.397 × weight (kg) + 4.799 × height (cm) − 5.677 × age (years)
Women: BMR = 447.593 + 9.247 × weight (kg) + 3.098 × height (cm) − 4.330 × age (years)
For the same 35-year-old, 165 cm, 68 kg woman from our Mifflin example: 447.593 + 628.8 + 511.2 − 151.6 ≈ 1,436 kcal/day — about 60 kcal above the Mifflin-St Jeor figure, a typical gap.
Why Mifflin replaced it
The 1919 sample skewed toward young, lean subjects, and modern populations carry more body fat — so Harris-Benedict tends to overestimate BMR by roughly 5% on average today, which is exactly the bias the 1990 Mifflin study set out to correct.
It remains useful as a cross-check: when both equations agree within ~100 kcal, you can trust the estimate band; when they diverge, body composition is probably unusual and Katch-McArdle is worth a look.
Put it into practice: run your own numbers with the related calculator — free, instant, and nothing leaves your browser.
Frequently asked questions
Should I use Harris-Benedict or Mifflin-St Jeor?
Default to Mifflin-St Jeor — validation studies favour it for modern populations. Harris-Benedict is a reasonable second opinion.
Why do the two formulas give different numbers?
They were fitted to different populations 70 years apart. The 100–150 kcal divergence is a window into how much uncertainty any equation carries.
Is the original 1919 version still used?
Rarely — virtually every modern calculator uses the 1984 Roza-Shizgal revision, which corrected the original coefficients with better data.
More guides
- What Is TDEE?
- What Is BMR?
- Mifflin-St Jeor Calculator
- Katch-McArdle Calculator
- BMR vs TDEE: What's the Difference?
- What Are MET Values?
- What Is NEAT?
- The Thermic Effect of Food
- Activity Multipliers Explained
- What Is a Calorie?
- Metabolic Adaptation Explained
- The Calorie Deficit, Explained
- 500-Calorie Deficit
- 1,000-Calorie Deficit
- 300-Calorie Deficit
- How Many Calories to Lose 1 Pound a Week
- How Many Calories to Lose 2 Pounds a Week
- Reverse Dieting
- Maintenance Phase
- Calorie Cycling
- How Accurate Are TDEE Calculators?
- Not Losing Weight in a Calorie Deficit? 7 Real Reasons
- Is 1,200 Calories a Day Safe?
- Should You Eat Back Exercise Calories?
- How Long Does Metabolic Adaptation Last?
- Do You Burn Fewer Calories as You Lose Weight?
- Why Your Maintenance Calories Keep Changing
- Calorie Cycling vs Flat Deficit
- How to Avoid Muscle Loss on GLP-1 Medications