Mifflin–St Jeor Equation Explained with a Worked Example
By Tools Star Hub Editorial Team · Published
Quick answer: the Mifflin–St Jeor equation estimates basal metabolic rate from body weight, height, age and sex. For men it is 10×kg + 6.25×cm − 5×age + 5. For women it is 10×kg + 6.25×cm − 5×age − 161. Multiply that BMR by an activity factor to estimate TDEE. Tools Star Hub’s TDEE Calculator and Alma’s calorie modules use this equation family in the browser. It is a strong desk-side estimate for many adults, not a substitute for clinical calorimetry or personalised medical advice.
Knowing the formula stops the calculator from feeling like a black box. When you can redo the arithmetic on paper, you catch unit mistakes faster and you understand why two people with the same weight can still land on different BMR values.
Where does the Mifflin–St Jeor equation come from?
Mifflin and colleagues published a predictive equation for resting energy expenditure in healthy individuals in The American Journal of Clinical Nutrition in 1990. The work compared measured resting expenditure with predictions based on easily collected anthropometrics.
Consumer tools adopted the equation because it needs only weight, height, age and sex—no body-fat device required. Later comparisons often find it among the better simple options for many adults, while still warning that individual error remains meaningful. That mix of convenience and relative accuracy is why Tools Star Hub documents the formula instead of hiding it behind a branded black box.
What are the exact formulas?
Weight enters in kilograms, height in centimetres and age in years. Sex selects which constant closes the equation. The Tools Star Hub calculators accept imperial inputs by converting pounds and inches first, then applying the metric form.
| Group | Formula (kcal/day) |
|---|---|
| Men | 10×weight(kg) + 6.25×height(cm) − 5×age(years) + 5 |
| Women | 10×weight(kg) + 6.25×height(cm) − 5×age(years) − 161 |
Worked example with the male formula
Use 80 kg, 180 cm and age 30. Compute 10×80 = 800. Compute 6.25×180 = 1,125. Compute 5×30 = 150. Then 800 + 1,125 − 150 + 5 = 1,780 kcal. That is the estimated BMR.
If the same person is sedentary, TDEE ≈ 1,780 × 1.2 = 2,136 kcal. If moderately active, TDEE ≈ 1,780 × 1.55 ≈ 2,759 kcal. The equation itself only produced the resting piece; the multiplier chose the daily piece.
Worked sketch with the female formula
Take 65 kg, 165 cm and age 28. Compute 10×65 = 650. Compute 6.25×165 = 1,031.25. Compute 5×28 = 140. Then 650 + 1,031.25 − 140 − 161 = 1,380.25 kcal, which tools typically round for display.
Multiplying by 1.375 for a lightly active week lands near 1,898 kcal of TDEE. Always re-check with the calculator rather than memorising one screenshot, especially after weight changes.
Why do weight, height, age and sex appear?
Heavier and taller bodies generally contain more metabolically active tissue, so those terms raise the estimate. Age enters with a minus sign because resting expenditure tends to decline across adulthood in group data. The sex-specific constants reflect average differences observed in the derivation samples.
The model is binary. Real people have more diverse biology than two constants can capture. Online tools that use Mifflin–St Jeor are transparent about that limit: they estimate, they do not declare your metabolism settled forever.
If your lived experience diverges a lot from the estimate—persistent unintended loss or gain while logging carefully—treat that as a signal to adjust intake and, when appropriate, to ask a clinician rather than to invent a new personal constant for the equation.
How does Mifflin–St Jeor differ from older equations?
Older popular equations such as Harris–Benedict also predict resting expenditure from anthropometrics, but they were derived from earlier samples and different methods. Many modern consumer calculators prefer Mifflin–St Jeor for general adult estimates.
You do not need to run three equations and average them. Pick one published method, learn its activity table, and judge it against your own multi-week outcomes. Switching formulas every few days creates noise that looks like “metabolism chaos.”
How do unit mistakes break the equation?
Entering 180 as kilograms when you meant 180 pounds, or typing height as 70 centimetres when you meant 70 inches, produces nonsense BMR values. Convert first. The Unit Converter and a careful read of the metric/imperial toggle prevent most of those errors.
Age should be whole years for this equation. If you are days away from a birthday and want precision, confirm the value with the Age Calculator, then type the year count the form expects.
What happens after BMR is known?
Activity multipliers turn BMR into TDEE. Maintain calories equal TDEE. Planning tools may subtract about 500 kcal for gradual loss or add about 300 kcal for a modest surplus. Suggested macros then split goal calories into protein, carbohydrate and fat percentages or into grams-per-kilogram protein targets.
Alma reuses the same resting-energy idea inside a broader nutrition workspace: food logging, micronutrient references and an educational coach. The equation is the shared foundation; the surrounding tools decide how you act on it.
When you change only the activity label, BMR stays put and TDEE moves. When you change weight, both BMR and TDEE move. Watching which input you edited helps you interpret a new result instead of assuming your metabolism suddenly flipped overnight.
What can the equation not see?
Muscle mass distribution, thyroid status, certain medications, recovery from illness, extreme ambient temperatures and adaptive changes after long dieting do not appear as fields. Two adults with identical inputs can still differ by hundreds of calories in measured resting expenditure.
Very low suggested intakes are inappropriate for many people. This site floors aggressive loss estimates at 1,200 kcal as a soft display bound. Adolescents, pregnant people and anyone with clinical concerns need professional guidance rather than equation-only planning.
How do I apply Mifflin–St Jeor safely?
- Gather metric measurements. Convert weight to kilograms and height to centimetres, or let the calculator convert imperial inputs for you.
- Select the matching sex constant. Use +5 at the end for the male formula or −161 for the female formula as published for this equation.
- Compute BMR, then multiply by activity. Write the resting value first. Only then apply 1.2–1.9 so you never confuse BMR with TDEE.
- Validate in the TDEE Calculator. Enter the same inputs online to confirm arithmetic, then adjust after two weeks of real-world feedback.
Example
Male sedentary path
80 kg, 180 cm, age 30 → BMR 1,780 kcal → ×1.2 → TDEE ≈ 2,136 kcal.
Imperial conversion first
140 lb and 5′6″ become kilograms and centimetres before any Mifflin term is evaluated.
Same BMR, higher activity
Keeping BMR fixed while moving from ×1.2 to ×1.55 raises TDEE by hundreds of calories without changing resting burn.
What should I keep in mind?
Published constants
Do not invent new end constants. The +5 and −161 values are part of the equation’s definition.
Rounding
Calculators may round to whole kilocalories. A difference of one or two kcal is not meaningful for planning.
Educational framing
Equation outputs support education and planning, not diagnosis or guaranteed rates of weight change.
Official paper
The original American Journal of Clinical Nutrition article is indexed on PubMed for readers who want the primary source.
FAQ
- Do I multiply by 10 before or after converting pounds to kilograms?
- Convert to kilograms first, then multiply by 10. Applying 10 to pounds and converting later breaks the formula.
- Is height entered in metres or centimetres?
- Centimetres in the standard Mifflin–St Jeor statement used here. One metre eighty is 180 cm, not 1.80 as the height term.
- Can teenagers use Mifflin–St Jeor from a website?
- Online adult equations are a poor stand-alone plan for adolescents. Growing bodies need clinical or dietetic guidance.
- Does the equation include the calories I burn at the gym?
- No. Gym and job costs enter only when you multiply BMR by an activity factor to estimate TDEE.
- Why is the female constant subtracted rather than added?
- That is how the published predictive equation was fitted to its sample. It is an empirical constant, not a judgement about individuals.
- Should I average Mifflin–St Jeor with another formula?
- Usually no. Averaging unrelated equations can hide assumptions. Stay with one method while you gather outcome data.
- How precise should my weight be for the equation?
- A consistent morning weight to the nearest 0.1–0.5 kg is enough. Obsessing over meal-to-meal scale noise does not improve the estimate.
- Can I rearrange the formula to solve for target weight?
- Not usefully for fat-loss planning. Change intake and activity from a current TDEE, then recalculate BMR as weight changes.
- Does Alma use a different resting equation?
- Alma’s calorie, BMR and TDEE modules follow the same Mifflin–St Jeor approach described for the dedicated TDEE Calculator.
- Where can I read the primary research citation?
- Search PubMed for the 1990 Mifflin resting energy expenditure paper, or use the PubMed link in the sources below.
Apply Mifflin–St Jeor with activity multipliers in the free TDEE Calculator.
Put the equation into a full daily method via how to calculate TDEE.
Separate resting and daily totals in BMR vs TDEE explained.
Confirm age in whole years with the Age Calculator.