Mifflin St Jeor Calculator

Your basal metabolic rate (BMR) is the energy your body burns at complete rest, and the Mifflin-St Jeor equation is the most accurate widely used way to estimate it without a lab. This calculator runs the exact equation published in 1990, converts pounds and inches if you prefer imperial units, multiplies by your activity level to get your total daily energy expenditure (TDEE), and turns that into a daily calorie target for losing, maintaining, or gaining weight.

Quick Answer

How to use this Mifflin-St Jeor calculator

Four choices and three numbers are all it takes. The result stays hidden until you press Calculate.

1. Pick your units and sex. Metric or imperial, and the men’s or women’s form of the equation. Switching units clears the weight and height fields on purpose, so a number typed for one system is never read in the other.
2. Enter age, weight, and height. All three must be above zero; the calculator names the field if one is missing or invalid.
3. Choose your activity level honestly. This single choice moves the answer more than any rounding does. One level too high adds roughly 200 to 300 calories you do not burn.
4. Choose a goal and press Calculate. You get your BMR, your TDEE, and the daily target with the goal applied, floored at 1,200 calories for women and 1,500 for men. Copy or share the three numbers, or press Reset to restore the worked example.

The Mifflin-St Jeor equation, checked against the original paper

The constants in the calculator are the ones Mifflin, St Jeor, and colleagues published in the American Journal of Clinical Nutrition in 1990, after measuring resting energy expenditure by indirect calorimetry in 498 healthy adults aged 19 to 78.

The published paper’s underlying regression used slightly less round coefficients (9.99 per kilogram, 4.92 per year, a single +166 term for men in place of the split constants). The authors simplified it into the two forms above and reported that the simplification did not change its predictive value, so the simplified forms are what every clinical tool, this one included, should use. Each term has a plain meaning:

Term	What it captures
10 × weight (kg)	Bigger bodies burn more at rest. Weight is the strongest single term.
6.25 × height (cm)	Taller bodies have more tissue and surface area to maintain.
− 5 × age (years)	Resting needs fall with age, largely through lost lean mass.
+5 (men) / − 161 (women)	The sex constant, standing in for average lean-mass differences at the same weight and height.

If you enter pounds and inches, the calculator converts first (pounds / 2.20462, inches × 2.54) and then runs the identical equation, so the imperial and metric answers for the same body match.

Worked example: BMR 1,724, TDEE 2,672, and all five goal targets

The prefilled values are a 35-year-old man, 80 kg, 175 cm, moderately active. His BMR by hand: (10 × 80) + (6.25 × 175) − (5 × 35) + 5 = 800 + 1,093.75 − 175 + 5 = 1,723.75, which the calculator rounds to 1,724 calories a day. Multiply by 1.55 for moderate activity: 1,723.75 × 1.55 = 2,671.81, shown as a TDEE of 2,672. Every goal target in the tool comes from that same TDEE:

Goal	Adjustment	Daily target
Lose weight (about 1 lb/week)	− 500	2,172 cal/day
Lose weight slowly (about 0.5 lb/week)	− 250	2,422 cal/day
Maintain weight	0	2,672 cal/day
Gain weight slowly	+ 250	2,922 cal/day
Gain weight (muscle building)	+ 500	3,172 cal/day

Each row reproduces exactly in the calculator by selecting that goal and pressing Calculate. Once you have a target, the macro calculator turns the calories into daily protein, carbohydrate, and fat grams.

Activity multipliers: the honest choice matters most

TDEE is BMR multiplied by one of five activity factors. These multipliers are conventions from clinical practice, not measurements of your life, and they are where most bad calorie targets come from.

Level	Multiplier	What it actually describes
Sedentary	1.2	Desk work, little or no planned exercise
Lightly active	1.375	Light exercise 1 to 3 days a week
Moderately active	1.55	Moderate exercise 3 to 5 days a week
Very active	1.725	Hard exercise 6 to 7 days a week
Extremely active	1.9	A physical job, or training twice a day

Training hard three times a week while sitting at a desk for the other 160 hours is usually “lightly active”, not “moderately active”. When in doubt, pick the lower level, follow it for two to three weeks, and adjust by 100 to 150 calories based on your weight trend. Long-term data points the same way: in the National Weight Control Registry, 54 percent of people who kept a large weight loss off report expending more than 2,000 calories a week in leisure-time activity, which is real work, not a dropdown label. People who track an active hobby such as cycling often sanity-check their training burn with a bicycle calorie calculator before trusting the top multipliers.

Setting your calorie target, and the floor this tool now enforces

Maintenance means eating at TDEE. The goal adjustments rest on the rough rule that a pound of body fat stores about 3,500 calories, so a daily 500-calorie deficit sums to about a pound a week. Treat that as a planning estimate, not a promise: as you lose weight your TDEE falls, and the same target produces slower loss.

One disclosure that matters. This calculator applies the goal adjustment exactly as chosen, then enforces a daily floor: 1,200 calories a day for women and 1,500 for men. A small, sedentary person who selects the fastest loss goal can be shown a target below 1,200 calories a day: enter a 19-year-old woman at 40 kg and 140 cm, sedentary, with the 1 lb/week goal, and the tool now prints the 1,200 floor instead of 723 calories a day. The 723 figure is the honest arithmetic of TDEE minus 500, but it is not a safe diet, so the floor replaces it and the result says so. Go below the floor only with medical supervision, as the CDC’s healthy weight guidance frames weight loss around sustainable habits rather than extreme restriction. For gaining, a 250 to 500 calorie surplus with progressive training adds mostly muscle; the bulking calories calculator plans that side in more detail.

How accurate is Mifflin-St Jeor, and how do the other equations compare?

No equation measures you; the good ones are just wrong by less. In the Frankenfield systematic review prepared for the Academy of Nutrition and Dietetics (2005), Mifflin-St Jeor landed within 10 percent of lab-measured resting metabolic rate in 82 percent of non-obese adults, the best rate among the equations reviewed, and it also performed best in adults with obesity. That is why dietitians treat it as the default, and why this page runs it exactly as published instead of blending formulas.

For scale, here is the worked example’s BMR under three equations. The first row is this calculator’s output. The other two are worked by hand for context only; this tool does not compute them.

Equation	BMR for the example man	Notes
Mifflin-St Jeor (1990)	1,724 cal/day	This calculator. Best validated for modern adults.
Harris-Benedict, revised (1984)	1,801 cal/day	Runs about 77 calories higher here; the 1919 original overestimated measured values by about 5 percent even in Mifflin’s own sample.
Katch-McArdle	1,752 cal/day	Needs lean body mass: 370 + 21.6 × lean kg. Shown at an assumed 20 percent body fat (64 kg lean), so the row moves with that assumption.

What competing calculators miss

• Calculator.net’s calorie calculator is thorough, with three equations and macro breakdowns, but the choice of equation is left to the user, and its default presentation buries which formula produced the headline number.
• TDEE-focused tools such as tdeecalculator.net are fast and clean, yet most show a single target with no BMR alongside it, so you cannot see how much of the number is resting burn and how much is the activity guess.
• Several BMR pages mislabel their math: at least one ranking “Mifflin” calculator actually runs the revised Harris-Benedict equations in its worked example while calling them Mifflin-style, which quietly shifts results by 50 to 80 calories.
• Almost none disclose the missing floor. Tools happily print three-digit daily targets for small, sedentary users who pick aggressive loss goals, with no warning anywhere on the page.
• The gap this page fills: the exact published 1990 constants, BMR and TDEE shown side by side, all five goal targets reproducible from one worked example, an explicit hand-labelled comparison with the rival equations, and the unfloored behaviour of rival tools stated in plain words with the safe minimums next to it.

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