TMB Mifflin-St Jeor

Mifflin-St Jeor: the modern BMR standard

Published in 1990, the Mifflin-St Jeor equation estimates Basal Metabolic Rate (BMR), which is the energy your body burns at complete rest. For men it's BMR = 10·kg + 6.25·cm − 5·age + 5; for women, BMR = 10·kg + 6.25·cm − 5·age − 161. Mifflin and colleagues arrived at it by re-running the older Harris-Benedict (1919) data against a modern population, which cut down the systematic overestimation. Expect an error of around ±200 kcal/day. The ACSM now points to it as the reference equation for healthy adults. A quick example — a 70 kg, 175 cm, 30-year-old man works out to 10·70 + 6.25·175 − 5·30 + 5 = 1,700 kcal/day.

Applications and context

Whether the work is clinical nutrition, body recomposition, diabetes management or planning calories around sport, Mifflin-St Jeor is usually where people start. Once you have BMR, multiply it by an activity factor — 1.2 for sedentary up to 1.9 for very active — to get your TDEE. From there you adjust calories for whatever you're after, be it losing fat, gaining lean mass or holding steady.

FAQ

Why is Mifflin-St Jeor preferred over Harris-Benedict? The 1919 dataset rested on a handful of subjects whose body composition doesn't match people today. Mifflin's sample of 498 subjects came back with lower mean errors, and it's what the ACSM references now.

How accurate is it? It lands within ±10% for roughly 80% of healthy adults. Accuracy slips at the extremes of body composition, whether that's very obese or very lean, so reach for Katch-McArdle if you know your body-fat %.

Does it work for children? No. For anyone under 18, turn to the Schofield or FAO/WHO equations. Mifflin-St Jeor was validated on adults aged 19–78.