BMR for Men Age 45-49 at 80 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 45 to 49-year-old man weighing 80 kg (176 lb), the Mifflin-St Jeor equation gives a BMR of 1,683 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.

By the late forties, resting metabolism has fallen by roughly 130 kcal a day since age 21 at the same weight and height, according to the Mifflin-St Jeor age term — and in practice the fall is often larger, because muscle mass and daily movement tend to decline at the same time. For women, perimenopause is commonly under way in this band, bringing shifts in fat distribution and appetite; for men, testosterone declines gradually and recovery from training slows. None of this makes weight management impossible, but it does make the quality of the plan more important than its size: a modest deficit plus muscle-preserving training beats a large deficit every time.

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 45 to 49-year-old man at 80 kg and 178 cm:

  • 10 × 80 kg = 800 kcal
  • 6.25 × 178 cm = 1,113 kcal
  • 5 × 47 years = 235 kcal
  • Constant: + 5 kcal

So BMR = 800 + 1,113 − 235 + 5 = 1,683 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 (47 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 1,482.5 kcal/day
70 kg 1,582.5 kcal/day
80 kg 1,682.5 kcal/day
90 kg 1,782.5 kcal/day
100 kg 1,882.5 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 80 kg (176 lb) BMR is 1,683 kcal a day, and the TDEE figures are correspondingly higher: a sedentary day still burns 2,019 kcal, and a moderately active day considerably more. A 500 kcal deficit from sedentary TDEE gives 1,519 kcal, well above the 1,500 kcal floor, so there is room to cut without going near very-low-calorie territory. The BMI at this height and weight is 25.2, in the overweight range. Joint-friendly activity — walking, cycling, swimming — is the best way to add expenditure at this weight without stressing knees and ankles.

How BMR changes with age

Holding weight (80 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 1,757.5 kcal/day
42 years 1,707.5 kcal/day
52 years 1,657.5 kcal/day
62 years 1,607.5 kcal/day
68 years 1,577.5 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 45 to 49-year-old man at 80 kg:

| Activity level | Multiplier | TDEE | |---|---| | | Sedentary | 1.2 | 2,019 kcal/day | | Lightly active | 1.375 | 2,313 kcal/day | | Moderately active | 1.55 | 2,608 kcal/day | | Very active | 1.725 | 2,902 kcal/day | | Extremely active | 1.9 | 3,197 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 1,519 kcal a day, a moderately active maintenance target would be 2,608 kcal a day, a moderately active cutting target would be 2,108 kcal a day, and a moderately active bulking target would be 2,908 kcal a day.

How to use the 1,683 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 approach at this age is to anchor on BMR, pick the activity multiplier that matches a genuine average week, and set a deficit of about 500 kcal a day — no more. Recalculate when weight changes by about 5 kg, because BMR falls by 10 kcal a day for every kilogram lost and a stale target stops working. Prioritise protein at each meal, two or three strength sessions a week, and sleep: short sleep raises appetite and makes a deficit harder to hold, and it is one of the most common reasons a plan fails in this age band.

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 1,514–1,851 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 estimate carries an error band of roughly ±10% and cannot see the factors that matter most in the late forties: muscle mass, hormonal status, thyroid function, medication and sleep. A muscular person will burn more at rest than the figure below; a sedentary person with little muscle will burn less. The equation also cannot tell you anything about body composition or health on its own — a BMR figure and a weight are not a health assessment. Pair the number with waist circumference, strength and blood markers, and talk to a clinician if a medical condition or medication is part of the picture.

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 45 to 49-year-old man weighing 80 kg?

Using the Mifflin-St Jeor equation with a height of 178 cm and age 47 years, BMR is 1,683 kcal/day: 10 × 80 + 6.25 × 178 − 5 × 47 + 5 = 1,683. 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 1,514–1,851 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.

Is a falling BMR in your late forties inevitable?

The age term itself is small — about 5 kcal a day per year — and the larger fall comes from muscle and activity, both of which you can influence. Resistance training two or three times a week preserves the muscle that keeps BMR up, and daily steps defend the activity side. People who keep training through their forties keep far more of their resting metabolism than people who stop.

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 2,108 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 80 kg, each 5 kg of weight change moves BMR by 50 kcal a day.

Should I eat less than 1,200 or 1,500 kcal a day to lose weight faster?

No. The safety floors are 1,200 kcal a day for women and 1,500 kcal a day for men, and going below them without medical supervision risks nutrient deficiency, muscle loss and hormonal disruption — and the weight lost is more likely to be muscle than fat. A 500 kcal deficit from an honest TDEE gives about 0.5 kg of fat loss a week, which is the sustainable rate for most people.

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.