BMR for Men Age 65+ at 90 kg — Mifflin-St Jeor

Every calorie target starts with basal metabolic rate (BMR): the energy the body spends at complete rest, keeping the heart beating, the lungs working and body temperature stable. For a man aged 65+ weighing 90 kg (198 lb), Mifflin-St Jeor puts that figure at 1,678 kcal/day at a height of 178 cm. The full working is shown below so you can check every step — the number is an estimate from a published equation, not a medical prescription.

Why does one number matter so much? Because TDEE — the figure every diet or muscle-gain plan is built on — is BMR times an activity multiplier, so any error in BMR is magnified. A BMR that is 150 kcal too high becomes a TDEE that is 180–285 kcal too high, and a cutting target built on it may not cut at all. The sections below lay out the formula, the worked example for this exact age and weight, the BMR table across body weights, and the TDEE table for all five activity levels.

After 65, the equation's age term removes 340 kcal a day or more, and muscle loss — sarcopenia — becomes the dominant story. Resting metabolism falls not just because of age but because the most metabolically active tissue is shrinking. At this age, BMR is best used alongside a protein target and a strength routine: roughly 1.6 g of protein per kilogram a day, spread across meals, plus resistance training two or three times a week, does more to protect health and independence than chasing the lowest possible calorie number. Any weight-loss plan at this age should be discussed with a clinician first.

Calculate your own BMR

Your weight, height and age are almost certainly different from the example here, so run your own numbers with the BMR calculator. It uses the same Mifflin-St Jeor equation shown on this page. To turn BMR into a daily calorie target, use the TDEE calculator, which applies the activity multipliers.

Related pages and tools:

The formula: Mifflin-St Jeor (1990)

The Mifflin-St Jeor equation is the most widely validated formula for estimating resting energy expenditure in adults. It was published by Mifflin et al. in the American Journal of Clinical Nutrition in 1990 (Mifflin MD et al., Am J Clin Nutr 1990;51(2):241–247), and it is the equation most calculators and many clinical settings use as a starting point. For men it is:

BMR = 10 × weight (kg) + 6.25 × height (cm) − 5 × age (years) + 5

For women the final term is −161 instead of +5. Working through the example for a 65+-year-old man at 90 kg and 178 cm (age 68 years, the middle of the band):

  • 10 × 90 kg = 900 kcal
  • 6.25 × 178 cm = 1,112.5 kcal
  • 5 × 68 years = 340 kcal
  • Constant: +5 kcal

So BMR = 900 + 1,112.5 − 340 + 5 = 1,678 kcal/day (rounded to the nearest whole calorie). Every term has a meaning: weight contributes the most because a larger body costs more energy to maintain; height adds a smaller amount; age subtracts, because resting metabolism declines slowly with age; and the sex constant reflects average differences in body composition between men and women at the same weight and height.

How BMR changes with weight

At the same age (68 years) and height (178 cm), BMR rises by exactly 10 kcal a day for every extra kilogram of body weight, because the weight term is 10 × weight:

Body weight BMR
50 kg 1,278 kcal/day
60 kg 1,378 kcal/day
70 kg 1,478 kcal/day
80 kg 1,578 kcal/day
90 kg 1,678 kcal/day
100 kg 1,778 kcal/day

That 10-kcal-per-kilogram slope is also why BMR falls as you lose weight. A man who drops 10 kg lowers BMR by about 100 kcal a day, and TDEE falls by 120–190 kcal a day depending on activity level. Calorie targets therefore need recalculating every 5 kg or so of weight change — a target set at your starting weight quietly becomes a smaller deficit, or even a surplus, as the weight comes off.

From BMR to daily calories: TDEE

BMR is what you burn at rest. Daily life adds movement, and TDEE is BMR multiplied by an activity factor — 1.2 for sedentary, 1.375 for lightly active, 1.55 for moderately active, 1.725 for very active and 1.9 for extremely active. For this 65+-year-old man at 90 kg:

Activity level Multiplier TDEE
Sedentary 1.2 2,014 kcal/day
Lightly Active 1.375 2,307 kcal/day
Moderately Active 1.55 2,601 kcal/day
Very Active 1.725 2,895 kcal/day
Extremely Active 1.9 3,188 kcal/day

A cutting target is usually TDEE minus about 500 kcal a day, and a bulking target is usually TDEE plus about 300–350 kcal a day — but never below the safety floor of 1,500 kcal a day (men) without medical supervision. For this person, a moderately active cutting target would be about 2,101 kcal a day, maintenance about 2,601 kcal a day, and a bulking target about 2,901 kcal a day.

How to use the 1,678 kcal figure

The 1,678 kcal figure is a starting point for planning, not a daily eating target. Eating at BMR while living a normal life creates a deficit equal to everything you do beyond lying still — usually far too large to sustain. Instead, take the TDEE row that matches your real week and set the goal from there: maintenance at TDEE, cutting at roughly TDEE minus 300–500 kcal, bulking at roughly TDEE plus 300–350 kcal, and never below 1,500 kcal a day without medical supervision.

The second use of the figure is as a reality check on other calculators. If a different tool gives you a BMR hundreds of calories away from 1,678 for the same inputs, one of the two is using a different formula or different inputs — most often a different height, or an equation such as Harris-Benedict that tends to run higher. The working above lets you see exactly which inputs produced this number, so you can compare like with like instead of guessing.

What BMR does not tell you

Mifflin-St Jeor is the best-validated predictive equation for most adults, but it is still a prediction with error bars of roughly ±10% for an individual. Two men of the same age, weight and height can differ by 150–200 kcal a day in measured resting metabolic rate, because the formula cannot see muscle mass, thyroid status, medication or recent dieting history. After a long period of dieting, measured BMR often runs below the prediction — metabolic adaptation — and after building muscle it can run above it.

The formula is also less reliable at the extremes: for very muscular men it underestimates, because muscle is more metabolically active than fat; for men with a high body-fat percentage it overestimates, for the same reason. It says nothing about health by itself — a high BMR is not a sign of fitness, and a low BMR is not a diagnosis. Use it with waist circumference, body-fat percentage and strength as the supporting evidence, and treat a large gap between the prediction and your real-world results (weight not moving at a calculated deficit, for example) as a reason to adjust the estimate, not to force the body to match the maths.

Frequently asked questions

What is the BMR of a 65+-year-old man weighing 90 kg?

Using the Mifflin-St Jeor equation with a height of 178 cm and age 68 years, BMR is 1,678 kcal/day: 10 × 90 + 6.25 × 178 − 5 × 68 + 5 = 1,678. Your own BMR will differ if your height or exact age differ; use the BMR calculator with your own measurements.

Is Mifflin-St Jeor the most accurate BMR formula?

For most adults it is the best-validated predictive equation available, which is why it is the standard choice for calculators and clinical use. It still carries an error of roughly ±10% for an individual, because it cannot see your muscle mass. Formulas that use body-fat percentage, such as Katch-McArdle, can do better for very muscular or very lean people — but only if the body-fat figure fed into them is accurate.

Does BMR fall with age?

Yes. The equation subtracts 5 kcal a day per year of age, so BMR falls by about 50 kcal a decade at the same weight and height. In practice the decline is often larger because muscle mass and daily activity tend to fall with age too. Resistance training is the most effective countermeasure, because it preserves the muscle that keeps resting metabolism up.

Should I eat at my BMR to lose weight?

No. BMR is the energy cost of lying still all day; eating at BMR while living a normal active life creates a deficit equal to everything you do beyond lying still, which is usually far too large and unsustainable. Set the target from TDEE instead — for this man, about 2,601 kcal a day at moderate activity — and never go below 1,500 kcal a day (men) without medical supervision.

How often should I recalculate my BMR?

Recalculate whenever your weight changes by about 5 kg, when your activity level changes for more than a few weeks, or at least once a year as you age. A target based on an old weight gradually stops working: as weight falls, BMR and TDEE fall with it, so a deficit set months ago shrinks over time.

What is my TDEE if I am moderately active at 90 kg?

Multiply BMR by 1.55: 1,678 × 1.55 = 2,601 kcal/day. That is the maintenance figure — the intake that, on average, holds weight steady at this activity level. A cutting target from there is about 2,101 kcal a day and a bulking target about 2,901 kcal a day, always staying above the 1,500 kcal safety floor.

Estimates only, not medical advice. Minimum safe intakes: 1,200 kcal/day women, 1,500 kcal/day men — consult a healthcare professional before a very-low-calorie diet.