The Mifflin-St Jeor Equation: A Complete Guide for Coaches
The go-to formula for estimating your clients' basal metabolic rate. Full formulas, Harris-Benedict comparison, three worked client profiles, and the limitations you need to know before building a meal plan.
What is the Mifflin-St Jeor equation?
The Mifflin-St Jeor equation is a formula published in 1990 that estimates Basal Metabolic Rate (BMR) from weight, height, age, and sex. It's considered the most accurate option for modern populations, with an average margin of error around 5%, compared to 10 to 15% for older formulas.
BMR is the energy your client burns at complete rest: breathing, blood circulation, body temperature regulation. This accounts for 60 to 75% of their total daily energy expenditure (TDEE). To get TDEE, you multiply BMR by an activity factor.
Formula for men
BMR = (10 x weight in kg) + (6.25 x height in cm) - (5 x age in years) + 5
Formula for women
BMR = (10 x weight in kg) + (6.25 x height in cm) - (5 x age in years) - 161
The only difference between the two formulas is the constant at the end: +5 for men, -161 for women. Everything else is identical. That simplicity makes it a quick tool to use during an initial consultation, even before moving on to the full TDEE calculation.
Mifflin-St Jeor vs Harris-Benedict: which should coaches use?
Mifflin-St Jeor is more accurate than Harris-Benedict for today's adults. Harris-Benedict, created in 1919 and revised in 1984, overestimates BMR by 5 to 15% in sedentary individuals. For a coach building meal plans, that overestimation means insufficient deficits and weight loss plateaus.
| Criteria | Mifflin-St Jeor | Harris-Benedict |
|---|---|---|
| Year published | 1990 | 1919 (revised 1984) |
| Average margin of error | ~5% | 5 to 15% |
| Target population | Modern adults (19-78 years) | 1919 population |
| Overestimation risk (sedentary) | Low | High (5 to 15%) |
| Coach recommendation | Primary formula | Cross-check |
Practical tip: calculate BMR with both formulas. If the results differ by more than 100 kcal, dig deeper into your client's activity questionnaire before picking a number.
How to calculate BMR with Mifflin-St Jeor: 3 client profiles
Here's the formula applied to three client profiles you'll see regularly in your practice. Each example walks through the BMR calculation, the activity multiplier, and the goal-based adjustment.
Profile 1: Sarah, office worker (sedentary)
Data: Female, 34 years old, 72 kg, 165 cm. Desk job 8 hours/day, no regular exercise.
Formula: (10 x 72) + (6.25 x 165) - (5 x 34) - 161
Calculation: 720 + 1,031.25 - 170 - 161 = 1,420 kcal (BMR)
TDEE: 1,420 x 1.2 (sedentary) = 1,704 kcal/day
Fat loss target: 1,704 - 350 = 1,354 kcal/day
Profile 2: James, sales rep on the road (moderately active)
Data: Male, 41 years old, 83 kg, 178 cm. On the move during the day, 3 weight training sessions per week.
Formula: (10 x 83) + (6.25 x 178) - (5 x 41) + 5
Calculation: 830 + 1,112.50 - 205 + 5 = 1,743 kcal (BMR)
TDEE: 1,743 x 1.55 (moderately active) = 2,702 kcal/day
Maintenance target: 2,702 kcal/day
Profile 3: Emma, triathlete (very active)
Data: Female, 27 years old, 58 kg, 170 cm. 6 training sessions per week (swimming, cycling, running).
Formula: (10 x 58) + (6.25 x 170) - (5 x 27) - 161
Calculation: 580 + 1,062.50 - 135 - 161 = 1,347 kcal (BMR)
TDEE: 1,347 x 1.725 (very active) = 2,324 kcal/day
Performance target: 2,324 + 200 = 2,524 kcal/day
These three profiles highlight a key point: the activity multiplier makes more difference than the formula itself. Sarah and Emma have similar BMRs (1,420 vs 1,347 kcal), but their TDEEs diverge by over 600 kcal. To split those calories into macros, check our macro calculation guide.
How do you pick the right activity multiplier?
The activity multiplier converts BMR into TDEE. It's the most subjective step in the calculation, and the most common source of error. Base it on your client's typical week, not their best week.
| Level | Multiplier | Typical profile |
|---|---|---|
| Sedentary | 1.2 | Desk job, no regular exercise |
| Lightly active | 1.375 | 1-3 sessions per week, moderate daily walking |
| Moderately active | 1.55 | 3-5 sessions per week, semi-active job |
| Very active | 1.725 | 6-7 sessions per week, physical job |
| Extremely active | 1.9 | Two-a-day training, professional athlete |
The most common mistake: overestimating activity level. A client who trains 4 times a week but sits at a desk 8 hours a day is "moderately active" (1.55), not "very active." NEAT (non-exercise activity: walking, stairs, daily movement) often accounts for 15 to 30% of total TDEE.
What are the limitations of the Mifflin-St Jeor equation?
The equation works well for most healthy adults, but it has blind spots in three specific cases. Spotting these situations early lets you adjust your approach and avoid meal plans that miss the mark.
Very muscular clients
The formula doesn't distinguish lean mass from fat mass. A bodybuilder at 95 kg and 10% body fat has a significantly higher BMR than someone at 95 kg and 35% body fat. For these clients, the Katch-McArdle formula (which factors in lean body mass) gives better results, provided you have a reliable body composition measurement.
Obese clients
Mifflin-St Jeor overestimates BMR when BMI exceeds 35 because fat mass contributes less to metabolism than lean mass. For a client with severe obesity, reduce the result by 5 to 10% or use "adjusted body weight" (a value between actual and ideal weight) in the formula.
Older adults (65 and above)
Metabolism declines with age beyond what the "age" variable in the formula captures. After 65, muscle loss (sarcopenia) accelerates the drop in BMR. Apply an additional 5 to 10% reduction and monitor weight closely during the first few weeks.
In all three cases, the equation still works as a starting point. The real adjustment comes from tracking: weekly weigh-ins, energy levels, training performance. No formula replaces 3 to 4 weeks of observation.
How Promealplan applies this formula automatically
Calculating BMR by hand for every client takes time, especially when you're recalculating every 4 to 6 weeks. Promealplan builds this step into the meal plan creation flow: enter the profile, and the algorithm handles the rest.
Enter the client profile
Weight, height, age, activity level, goal, and dietary preferences. The algorithm calculates BMR, TDEE, and calorie targets automatically.
Meal plan generation
The algorithm selects from 1,000+ dietitian-validated recipes to hit the calorie target, macro split, and dietary constraints.
Adjust and deliver
Swap meals if needed, export as a branded PDF with an integrated grocery list. When the client progresses, update their profile and regenerate an adjusted plan in a few clicks.
Save time on BMR and macro calculations
Promealplan calculates BMR, TDEE, splits macros, and generates complete meal plans in minutes. 1,000+ validated recipes. Branded PDF export. Free to try, 3 plans, no credit card.
Try Promealplan for free →Frequently Asked Questions
What's the difference between BMR and TDEE?
How often should I recalculate a client's BMR?
Does Mifflin-St Jeor work for obese clients?
Can I use Mifflin-St Jeor for teenagers?
How do I go from BMR to an actual meal plan?
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Conclusion
The Mifflin-St Jeor equation is the most reliable formula for estimating BMR in a coaching context. Learn the formula, pick the right activity multiplier, spot the profiles that need adjustments, and your clients will progress faster. To turn that BMR into a working meal plan, move on to macro calculation.
Key Takeaways
- 1. Use Mifflin-St Jeor as your primary BMR formula
- 2. Cross-check with Harris-Benedict when the gap seems large
- 3. The activity multiplier matters more than the formula itself
- 4. Adjust for muscular, obese, or older clients
- 5. Recalculate every 4 to 6 weeks