BMR for Women Age 55-59 at 90 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 55 to 59-year-old woman weighing 90 kg (198 lb), the Mifflin-St Jeor equation gives a BMR of 1,485 kcal/day, worked step by step below using a height of 165 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 how it converts into daily calorie needs at each activity level.

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 women it is:

BMR = 10 × weight (kg) + 6.25 × height (cm) − 5 × age (years) − 161

For men the final term is +5 instead of −161. Working through the example for a 55 to 59-year-old woman at 90 kg and 165 cm:

  • 10 × 90 kg = 900 kcal
  • 6.25 × 165 cm = 1,031 kcal
  • 5 × 57 years = 285 kcal
  • Constant: −161 kcal

So BMR = 900 + 1,031 − 285 − 161 = 1,485 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 (57 years) and height (165 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 1,085 kcal/day
60 kg 1,185 kcal/day
70 kg 1,285 kcal/day
80 kg 1,385 kcal/day
90 kg 1,485 kcal/day
100 kg 1,585 kcal/day

That 10-kcal-per-kilogram slope is also why BMR falls as you lose weight. A woman 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 55 to 59-year-old woman at 90 kg:

Activity level Multiplier TDEE
Sedentary 1.2 1,782 kcal/day
Lightly Active 1.375 2,042 kcal/day
Moderately Active 1.55 2,302 kcal/day
Very Active 1.725 2,562 kcal/day
Extremely Active 1.9 2,822 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 1,200 kcal a day (women) without medical supervision. For this person, a sedentary cutting target would be 1,282 kcal a day, and a moderately active maintenance target would be 2,302 kcal a day.

How to use the 1,485 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.

Recalculate when the inputs change. Age moves slowly, but weight can move several kilograms in a few months, and activity can change with a new job, a new training programme or a season. Each recalculation takes a minute and keeps the target honest. And remember that BMR is only one side of the energy-balance equation: the other side is what you actually eat, which is why tracking food intake for two to three weeks is the fastest way to find out whether an estimate matches reality.

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. 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 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 55 to 59-year-old woman weighing 90 kg?

Using the Mifflin-St Jeor equation with a height of 165 cm and age 57 years, BMR is 1,485 kcal/day: 10 × 90 + 6.25 × 165 − 5 × 57 − 161 = 1,485. 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, and never go below 1,200 kcal a day (women) 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.

Why is my BMR lower than my friend's when we weigh the same?

Height, age and sex all shift the result, and muscle mass shifts it further even when the formula cannot see it. A taller person has a higher BMR than a shorter person at the same weight, a younger person higher than an older person, and a more muscular person higher than a less muscular person of the same weight — the equation captures the first three and misses the fourth.

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.