Why We Use the Mifflin-St Jeor Equation for Calorie Targets
Not all calorie calculators are equal. We break down why Mifflin-St Jeor is the gold standard and how Mealio applies it.
Every calorie calculator is estimating the same thing: how much energy you burn at rest. They differ in which equation they use, and the differences are not trivial.
What the equation actually computes
Mifflin-St Jeor estimates Basal Metabolic Rate — the energy your body uses doing nothing at all:
That figure is then multiplied by an activity factor to get maintenance calories, and adjusted up or down for your goal.
Why not Harris-Benedict?
Harris-Benedict came first, in 1919, and was revised in 1984. It is still the default in a lot of older calculators. The problem is its source data: it was derived from a small, young, lean sample that does not represent most people using it now, and it tends to overestimate BMR — commonly by around 5%.
Mifflin-St Jeor was published in 1990 against a larger and more varied sample, and validation studies have repeatedly found it closer for the general population. That is why it is the one dietitians reach for by default.
Where every equation breaks down
Be clear about what these numbers are. They are population averages, and individuals vary around them by roughly ±10% — occasionally more.
They are least reliable for:
If you know your body-fat percentage, the Katch-McArdle formula uses lean mass instead and will be more accurate for you.
How to use the number properly
Treat the output as a starting hypothesis, not a measurement. The right approach:
Your own trend data beats any equation within a month. The equation exists to give you a sensible place to start, not a number to obey.
What Mealio does with it
The calculator applies Mifflin-St Jeor with the activity level you pick, then splits the result into protein, carbohydrate and fat targets. Those targets propagate to your dashboard, your plans and the recipe pages — so the figure you see when planning is the same one the generator is aiming at.