How it works
Mifflin–St Jeor: BMR = 10·kg + 6.25·cm − 5·age + s (s = +5 men, −161 women); TDEE = BMR × activity factor
The Mifflin–St Jeor equation estimates resting energy from weight in kilograms, height in centimetres and age in years, with a sex constant of +5 for men and −161 for women. A 30-year-old man weighing 80 kg at 180 cm has a BMR of 10·80 + 6.25·180 − 5·30 + 5 = 800 + 1125 − 150 + 5 = 1,780 kcal/day. We also show the revised 1984 Harris–Benedict figure (for men, 88.362 + 13.397·kg + 4.799·cm − 5.677·age) as a second opinion — the two usually land within a few percent. TDEE comes from multiplying BMR by a standard physical-activity level: 1.2 sedentary, 1.375 light, 1.55 moderate, 1.725 active and 1.9 very active. We convert pounds and inches internally so the result is identical whichever units you choose. Mifflin–St Jeor is the more accurate of the two on modern populations, which is why it is the headline number.
Sources
- Mifflin–St Jeor equation Mifflin MD, St Jeor ST, Hill LA, Scott BJ, Daugherty SA, Koh YO. A new predictive equation for resting energy expenditure in healthy individuals. Am J Clin Nutr. 1990;51(2):241–247.
- Harris–Benedict, revised Roza AM, Shizgal HM. The Harris Benedict equation reevaluated: resting energy requirements and the body cell mass. Am J Clin Nutr. 1984;40(1):168–182.
- Activity multipliers (PAL) Total daily energy expenditure is estimated as BMR × a physical-activity level (PAL): ~1.2 sedentary to ~1.9 very active, a convention used widely in dietetics.
FAQ
What is BMR and how is it calculated?
Basal Metabolic Rate is the calories your body uses at rest to keep you alive. This calculator uses the Mifflin–St Jeor equation: 10 × weight(kg) + 6.25 × height(cm) − 5 × age, plus 5 for men or minus 161 for women. It also shows the revised Harris–Benedict estimate alongside it.
What is the difference between BMR and TDEE?
BMR is energy burned at complete rest. TDEE (Total Daily Energy Expenditure) is BMR multiplied by an activity factor (1.2 sedentary up to 1.9 very active) and reflects everything you do in a day, including training. TDEE is the better target for working out how much to eat to maintain weight.
Which formula is more accurate, Mifflin–St Jeor or Harris–Benedict?
Mifflin–St Jeor (1990) is generally the more accurate of the two on modern populations, which is why it is the headline figure here. The revised Harris–Benedict (Roza & Shizgal, 1984) is shown as a cross-check; the two usually agree within a few percent.
How many calories should a runner eat?
Use your TDEE as the maintenance baseline, then adjust. Endurance training raises your needs, so an active runner often sits at the higher activity multipliers. Chronically eating below your needs harms recovery, hormones and bone health — see how much a single run burns with the running calories calculator and fuel accordingly.
Does BMR change with age?
Yes. BMR tends to fall gradually with age, partly from losing muscle, which is why age is in the equation. Staying strong and active slows that decline. The calculator factors age in directly, so re-run it as your age, weight or training change.
Should I eat below my BMR to lose weight?
Generally no. Eating below BMR for any length of time is aggressive and can backfire by slowing metabolism and harming health, especially for active people. A modest deficit from your TDEE — not your BMR — is the usual sustainable approach. Talk to a professional before any significant change.
BMR and TDEE are population estimates, not measurements — your real metabolism can vary by 10% or more from any formula. These figures are for general information and education, not medical or dietary advice. Do not use them to drive aggressive calorie restriction; consult a qualified doctor or dietitian about your energy needs, especially if you train hard.