BMR calculator

Estimate the calories your body needs at complete rest using the Mifflin-St Jeor equation — the current standard for basal metabolic rate.

How this calculator works

Basal metabolic rate is the energy your body uses for the things you cannot switch off: breathing, circulation, brain activity, cell repair and temperature control. It is measured in a rested, fasted state and typically accounts for 60–70% of daily calorie expenditure. The Mifflin-St Jeor equation used here replaced the older Harris-Benedict formula as the standard because it is more accurate across modern populations.

The result assumes no activity at all. Multiply it by an activity factor to get maintenance calories (the TDEE calculator does this). BMR falls with age and with loss of muscle mass, and rises with more muscle and a larger body. That is why two people of the same weight can have noticeably different BMRs, and why resistance training is valuable for long-term weight management.

The formula

Mifflin-St Jeor, metric inputs:

To use pounds and inches, convert first: 1 lb = 0.4536 kg, 1 in = 2.54 cm. The sedentary maintenance figure compounds BMR by the 1.2 activity factor.

Worked example

A 30-year-old Male with the default measurements has a BMR of 1,783 calories a day — about 74.3 calories an hour at complete rest. Doing nothing but sitting all day, maintenance would be around 2,139 calories.

Common mistakes

• Eating below BMR for long periods. Severe restriction encourages muscle loss and lowers BMR, making weight regain more likely.
• Treating BMR as maintenance. Any movement — walking, working, even fidgeting — adds to it. Use TDEE for a spending budget.
• Assuming the equation is exact. Individual variation is usually within about 10%, but thyroid conditions, some medications and very high muscle mass can shift it further.