BMR for Men Age 18-24 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 18 to 24-year-old man weighing 80 kg (176 lb), the Mifflin-St Jeor equation gives a BMR of 1,813 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.

At 18 to 24, resting metabolism is close to its lifetime peak. Growth is finishing, muscle mass is still being built, and most people in this age band are more active than they will be at any later age — walking between classes, playing sport, working on their feet. That activity is not part of BMR, but it is why the TDEE figures below are often higher for this group than for older adults at the same weight. The BMR figure itself is still only the resting cost, and it is the anchor every calorie target is built from.

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 18 to 24-year-old man at 80 kg and 178 cm:

  • 10 × 80 kg = 800 kcal
  • 6.25 × 178 cm = 1,113 kcal
  • 5 × 21 years = 105 kcal
  • Constant: + 5 kcal

So BMR = 800 + 1,113 − 105 + 5 = 1,813 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 (21 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 1,612.5 kcal/day
70 kg 1,712.5 kcal/day
80 kg 1,812.5 kcal/day
90 kg 1,912.5 kcal/day
100 kg 2,012.5 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 1,813 kcal a day, and the TDEE figures are correspondingly higher: a sedentary day still burns 2,175 kcal, and a moderately active day considerably more. A 500 kcal deficit from sedentary TDEE gives 1,675 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 18 to 24-year-old man at 80 kg:

| Activity level | Multiplier | TDEE | |---|---| | | Sedentary | 1.2 | 2,175 kcal/day | | Lightly active | 1.375 | 2,492 kcal/day | | Moderately active | 1.55 | 2,809 kcal/day | | Very active | 1.725 | 3,127 kcal/day | | Extremely active | 1.9 | 3,444 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 1,675 kcal a day, a moderately active maintenance target would be 2,809 kcal a day, a moderately active cutting target would be 2,309 kcal a day, and a moderately active bulking target would be 3,109 kcal a day.

How to use the 1,813 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.

For most people in this age band the practical question is not whether to eat less, but whether the target matches a lifestyle that changes quickly. A student timetable, a first job, a new training routine or a season of sport can each move daily activity by a whole multiplier step — the difference between lightly active and moderately active is more than 200 kcal a day at this weight. Re-run the calculation when the routine changes, and treat strength training as the best investment available at this age: muscle built now raises resting metabolism for decades, while crash diets in the late teens and early twenties are the fastest way to lose muscle and slow the metabolism down.

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 1,631–1,994 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.

The formula's blind spot matters most at this age for people who train seriously. A 20-year-old who lifts four times a week and carries visibly more muscle than average will burn more at rest than the equation predicts, because the equation only sees total weight — it cannot tell 80 kg of muscle from 80 kg of fat. The reverse applies to a sedentary person of the same weight with little muscle. The ±10% error band around the figure below covers most of that, but if you are unusually muscular or unusually sedentary for your weight, treat the estimate as a starting point and adjust from two or three weeks of 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 18 to 24-year-old man weighing 80 kg?

Using the Mifflin-St Jeor equation with a height of 178 cm and age 21 years, BMR is 1,813 kcal/day: 10 × 80 + 6.25 × 178 − 5 × 21 + 5 = 1,813. 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 1,631–1,994 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 my BMR at its highest in my early twenties?

Nearly. The equation subtracts 5 kcal a day for every year of age, so BMR at the same weight and height is about 50 kcal a day lower at 32 than at 21, and about 235 kcal lower at 68. The bigger change over the twenties is usually activity, not BMR: the move from an active student life to a desk job can cut daily expenditure by several hundred calories even though BMR itself barely moves.

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 2,309 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.

I train hard — should I use a higher activity multiplier?

Only if the training is genuinely frequent and intense. Three moderate gym sessions a week on top of a desk job is lightly active, not very active. Very active means hard training most days plus an active job or lifestyle. Overstating activity is the most common reason a maintenance target comes out too high, so pick the level that describes a typical week, not your best week.

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.