BMR for Men Age 35-39 at 70 kg — Mifflin-St Jeor

Basal metabolic rate (BMR) is the energy your body uses at complete rest — to keep your heart beating, your lungs breathing, your body warm and your cells maintained — before any movement, digestion or exercise is counted. For a 35 to 39-year-old man weighing 70 kg (154 lb), the Mifflin-St Jeor equation gives a BMR of 1,633 kcal/day, worked step by step below using a height of 178 cm. That figure is an estimate built from a published formula, not a personal prescription.

BMR is the foundation of every calorie target. Total daily energy expenditure (TDEE) is BMR multiplied by an activity factor, and cutting, maintenance and bulking targets are all set relative to TDEE. Getting BMR right therefore matters more than it looks: a 200 kcal error in BMR becomes a 200–380 kcal error in TDEE once the activity multiplier is applied. This page shows the calculation in full so you can check it, and shows how the same person's BMR changes with weight and age, and how it converts into daily calorie needs at each activity level.

In the late thirties the slow decline in resting metabolism becomes measurable, even though it is still small: the Mifflin-St Jeor equation subtracts 5 kcal a day per year of age, so BMR at 37 is about 80 kcal lower than at 21 at the same weight and height. The more important change is usually muscle. Without regular strength training, adults lose muscle gradually from their thirties onward, and because muscle costs more energy at rest than fat, that loss pulls BMR down further than the age term alone suggests. The figure below is therefore best read alongside a plan to keep muscle, not just a calorie target.

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 35 to 39-year-old man at 70 kg and 178 cm:

  • 10 × 70 kg = 700 kcal
  • 6.25 × 178 cm = 1,113 kcal
  • 5 × 37 years = 185 kcal
  • Constant: + 5 kcal

So BMR = 700 + 1,113 − 185 + 5 = 1,633 kcal/day. 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 (37 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
60 kg 1,532.5 kcal/day
70 kg 1,632.5 kcal/day
80 kg 1,732.5 kcal/day
90 kg 1,832.5 kcal/day
100 kg 1,932.5 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.

At 70 kg (154 lb) this is the middle of the weight range, and the arithmetic is straightforward: a sedentary TDEE of 1,959 kcal a day gives a cutting target of 1,500 kcal, comfortably above the 1,500 kcal safety floor, and a moderately active maintenance figure that leaves real room for food. The BMI at this height and weight is 22.1, in the healthy weight range. This is the weight band where a 500 kcal deficit is most sustainable, because the target stays high enough to include adequate protein and variety.

How BMR changes with age

Holding weight (70 kg) and height (178 cm) fixed, the age term alone lowers BMR by 5 kcal a day for every year. The table below shows the same man's BMR at different ages:

Age BMR
21 years
32 years 1,657.5 kcal/day
42 years 1,607.5 kcal/day
52 years 1,557.5 kcal/day
62 years 1,507.5 kcal/day
68 years 1,477.5 kcal/day

The gap between 21 and 68 is 235.0 kcal a day — real, but smaller than most people expect. What makes the difference larger in practice is that muscle mass and daily activity usually fall at the same time as age rises, and the equation cannot see either of those. That is why two people of the same sex, age, height and weight can have quite different resting metabolisms, and why the training and activity advice on this page matters as much as the number itself.

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 35 to 39-year-old man at 70 kg:

| Activity level | Multiplier | TDEE | |---|---| | | Sedentary | 1.2 | 1,959 kcal/day | | Lightly active | 1.375 | 2,245 kcal/day | | Moderately active | 1.55 | 2,530 kcal/day | | Very active | 1.725 | 2,816 kcal/day | | Extremely active | 1.9 | 3,102 kcal/day | |

A cutting target is usually TDEE minus about 500 kcal a day, and a bulking target is usually TDEE plus about 300 kcal a day — but never below the safety floor of 1,500 kcal a day (men) without medical supervision. For this person, a sedentary cutting target would be 1,500 kcal a day (the safety floor binds here, because TDEE minus 500 would be below it), a moderately active maintenance target would be 2,530 kcal a day, a moderately active cutting target would be 2,030 kcal a day, and a moderately active bulking target would be 2,830 kcal a day.

How to use the 1,633 kcal figure

Use BMR as the anchor, not the target. Nobody should eat at BMR for long: it is the cost of lying still all day, and daily life always adds to it. The practical use of BMR is to build a TDEE estimate honestly — pick the activity level that matches a typical week, not your best week — and then set a goal target from TDEE. If you sit most of the day and train three times a week, you are closer to lightly active than moderately active, and the higher multiplier inflates the target by well over 100 kcal a day.

The practical use of this number is to set a TDEE target that reflects a real week, then to defend it with training. Pick the activity multiplier honestly — a desk job plus three gym sessions is lightly active, not moderately active — and recalculate when weight changes by about 5 kg, because a target set at a heavier weight quietly becomes a smaller deficit as weight falls. Two or three weekly strength sessions, enough protein spread across meals, and a daily step target are the three habits that protect resting metabolism through the late thirties and beyond.

What BMR does not tell you

A BMR estimate is a population average, not a measurement. Individual resting metabolic rate varies by roughly ±10% around the Mifflin-St Jeor prediction because of differences in muscle mass, genetics, thyroid function and health — for this person that means a plausible range of roughly 1,469–1,796 kcal a day. The equation uses total body weight, so it is less accurate for very muscular people (it underestimates, because muscle burns more at rest than fat) and for people with a high body-fat percentage (it overestimates). The only way to measure BMR directly is indirect calorimetry in a laboratory, which is rarely available outside research or clinical settings.

This is an estimate with an error band of roughly ±10%, and the equation cannot see the things that matter most at this age: muscle mass, body-fat percentage, thyroid function, sleep quality and stress. A muscular person at this weight will burn more at rest than the figure below, and a sedentary person with little muscle will burn less. Direct measurement of resting metabolic rate needs indirect calorimetry in a laboratory, which is rarely available outside research or clinical settings — so the honest approach is to treat the estimate as a starting point and adjust from tracked intake and weight change.

The equation also cannot tell you anything about body composition, fitness or health on its own. A high BMR can belong to a muscular athlete or to a larger person with a high body-fat percentage; a low BMR can belong to a small, healthy person or to someone whose metabolism has adapted downward after a long period of very low intake. Pair BMR with other measures — waist circumference, body-fat estimates, strength, blood markers — before drawing conclusions about health. And never use BMR as an eating target: eating at or below BMR for an extended period without medical supervision risks nutrient deficiency, muscle loss and hormonal disruption.

Frequently asked questions

What is the BMR of a 35 to 39-year-old man weighing 70 kg?

Using the Mifflin-St Jeor equation with a height of 178 cm and age 37 years, BMR is 1,633 kcal/day: 10 × 70 + 6.25 × 178 − 5 × 37 + 5 = 1,633. 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 — for this person that means a plausible range of about 1,469–1,796 kcal a day. 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.

How much does BMR fall between 35 and 40?

The equation itself accounts for about 25 kcal over those five years — 5 kcal per year. In real life the fall is often larger, because muscle mass and daily activity tend to fall at the same time. That is why the advice for this age band is always the same: keep the muscle with resistance training, keep the steps up, and recalculate the target as weight changes rather than blaming the number.

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 person, a moderately active cutting target is about 2,030 kcal a day — 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 — 10 kcal of BMR per kilogram — so a deficit set months ago shrinks over time. At 70 kg, each 5 kg of weight change moves BMR by 50 kcal a day.

Is it harder to lose weight at 37 than at 27?

Somewhat, but the difference is smaller than people expect. BMR is only about 80 kcal lower than at 21 at the same weight, and a 500 kcal daily deficit still produces roughly 0.5 kg of fat loss a week. What usually changes is lifestyle: less free time, more sitting, poorer sleep. A smaller, sustainable deficit plus strength training beats a large deficit that cannot be maintained.

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.