Average BMR by age and gender

Average BMR is roughly 1,200 to 1,450 kcal a day for women and 1,550 to 1,850 kcal a day for men of typical size, falling by about 50 kcal per decade of age. Using the Mifflin-St Jeor equation, a 30-year-old woman of 165 cm and 65 kg has a BMR of about 1,370 kcal, and a 30-year-old man of 178 cm and 80 kg about 1,768 kcal.

Basal metabolic rate, or BMR, is the energy your body uses at complete rest to keep the heart beating, the lungs working and cells alive. It is the largest single part of daily energy use for most people, which is why it sits at the centre of every calorie calculator.

BMR chart by age, gender and weight

There is no single average BMR, because it depends so strongly on body size. The chart below calculates BMR with the Mifflin-St Jeor equation for women of 165 cm (5 ft 5 in) and men of 178 cm (5 ft 10 in) at three body weights each. Find the column closest to your weight.

Read across a row and the gap between the sexes is clear. Read down a column and age has a steady, modest effect. Move across columns of the same sex and weight has the largest effect of all.

The formula behind the chart

• Men: BMR = 10 x weight (kg) + 6.25 x height (cm) - 5 x age + 5
• Women: BMR = 10 x weight (kg) + 6.25 x height (cm) - 5 x age - 161

A 45-year-old man who is 183 cm and 95 kg: 950 + 1,143.75 - 225 + 5 = 1,874 kcal. A 45-year-old woman who is 160 cm and 58 kg: 580 + 1,000 - 225 - 161 = 1,194 kcal.

Why men and women differ

Men on average have more lean mass and less fat mass at the same body weight, and lean tissue drives most of resting energy use. The equation captures that with a fixed offset of 166 kcal. In reality the gap varies: a muscular woman can easily have a higher BMR than a less muscular man of the same weight.

Mifflin-St Jeor versus Harris-Benedict

The older Harris-Benedict equation, revised in 1984, usually gives numbers 50 to 90 kcal higher for these profiles. Our BMR calculator shows both.

Does BMR really drop with age?

The equation lowers BMR by 5 kcal per year. Measured data suggest most of that decline reflects changes in body composition, not a slower engine. Size-adjusted energy expenditure looks stable from about 20 to 60, then declines slowly.

Strength training, enough protein and staying active are the most effective ways to keep resting energy use from falling faster than it needs to.

What BMR can and cannot tell you

• It is an estimate for a typical body. Muscular people tend to be underestimated and people with more body fat overestimated.
• If you know your body fat percentage, the Katch-McArdle equation, which uses lean mass, may fit better.
• BMR is not your daily calorie need. Multiply it by an activity factor from 1.2 to 1.9 to get TDEE.
• Eating below your BMR for a while is not automatically dangerous, but it usually means the deficit is larger than it needs to be.

From BMR to daily calorie needs

To turn BMR into a daily target, multiply it by an activity factor: 1.2 if you are sedentary, 1.375 for light activity, 1.55 for moderate exercise three to five days a week and 1.725 for hard daily training. A 40-year-old woman of 65 kg with a BMR of 1,320 kcal who exercises three times a week needs about 2,046 kcal a day. A man of 80 kg and the same age with a BMR of 1,718 kcal needs about 2,662 kcal.

Our TDEE calculator does this step for you. If you are aiming to lose weight, subtract around 500 kcal from TDEE rather than from BMR.

What else affects BMR

• Lean mass: the more muscle and organ tissue you carry, the higher your resting burn.
• Thyroid function: an underactive or overactive thyroid can shift BMR noticeably and needs medical assessment.
• Illness and fever raise resting energy use temporarily.
• Very low calorie intake over weeks lowers it modestly, beyond what weight loss alone explains.
• Pregnancy raises it, particularly in the third trimester.

Can you measure your BMR?

Yes. Indirect calorimetry measures the oxygen you use and the carbon dioxide you produce while you lie still, usually after an overnight fast, and converts that into energy expenditure. Some clinics, universities and sports labs offer it. It is more accurate than any equation for an individual, but results still vary with sleep, stress, recent meals and the menstrual cycle, so a single test is a snapshot rather than a fixed number. For most people, an equation plus a few weeks of weight tracking is accurate enough to plan from.