Mifflin-St Jeor vs Harris-Benedict

Mifflin-St Jeor and Harris-Benedict are trying to do exactly the same thing: take your weight, height, age and sex and turn them into a single Basal Metabolic Rate, the calories you would burn lying still for a day. What separates them is not the kind of arithmetic — both are a short line of multiplication and addition — but the people whose measurements the coefficients were tuned against. Harris-Benedict is the older of the pair, first published in 1919 and given a refreshed set of constants in the 1984 revision that most tools now use. Mifflin-St Jeor arrived in 1990, fitted to a more recent and more varied sample of adults. Because each equation simply encodes the average relationship found in its own dataset, the two carry slightly different assumptions about how a given body burns energy. Neither is measuring you directly; both are reading off a curve drawn through other people decades apart. That shared structure is why you can drop the very same height, weight, age and sex into either one and get an answer in the same units — and why the choice between them is a question of which historical sample you would rather lean on, not which one is doing something fundamentally cleverer with your numbers.

For most modern adults the two equations land close together, with Harris-Benedict tending to read a little high. The gap at the BMR level is usually small — often under about a hundred calories, which is less than a single snack and well inside the margin either formula carries against a laboratory measurement. Put plainly, the formula you pick rarely moves your estimate by more than a rounding error. What moves it far more is the activity multiplier you apply afterward: the difference between a sedentary 1.2 and a moderately active 1.55 dwarfs the difference between the two BMR equations, because that factor scales the whole figure rather than nudging its base. Choosing an honest activity level, and resisting the temptation to round it upward, will shape your daily total more than any debate over which historical curve to use. So if you find yourself hesitating between Mifflin-St Jeor and Harris-Benedict, the more useful question is whether you have described your week accurately. The TDEE Calculator is the full tool behind this page, laying out every activity tier so you can see how much the multiplier — not the formula — drives the number you plan meals around.

Seeing the comparison for your own body takes a single extra step. The calculator opens on Mifflin-St Jeor, so enter your sex, age, height and weight and read the first figure; then switch the formula selector to Harris-Benedict and recalculate to get the second number for exactly the same inputs. Placing the two results side by side is the quickest way to settle the question for yourself — most people are surprised by how narrow the gap turns out to be. If you would rather read each formula on its own dedicated page, the Mifflin-St Jeor Calculator walks through the 1990 equation, and the Harris-Benedict Calculator covers the older revised one. Whichever you settle on, treat the output as a grounded starting estimate rather than a precise reading: hold to it for a couple of weeks, watch how your weight actually responds, and adjust your intake instead of switching formulas in search of a better number. These figures are general estimates for healthy adults, not medical advice.