What is basal metabolic rate?
Basal metabolic rate, or BMR, is an estimate of the energy your body uses at rest for basic functions such as breathing, circulation and temperature control.
Basal metabolic rate means the calories your body is estimated to use at complete rest. It is the background energy cost of keeping essential body processes running.
BMR is not the same as your total daily calorie need. It does not include walking, work, exercise, digestion or everyday movement. Those extra layers are added later when estimating TDEE, or total daily energy expenditure.
Why BMR matters
BMR is the starting point for many calorie calculators. Once a calculator estimates your resting energy use, it applies an activity multiplier to estimate your daily calorie needs.
This is why two people with the same body weight can have different calorie estimates. Height, age, sex, body size and activity level all affect the final number.
Estimate your daily calories
Use the calorie calculator to estimate BMR, maintenance calories and goal-based calorie targets.
How BMR is estimated
Most online calorie tools estimate BMR using an equation rather than directly measuring it in a lab. A common modern equation is the Mifflin-St Jeor formula.
Male estimate:
BMR = 10 × weight(kg) + 6.25 × height(cm) - 5 × age + 5
Female estimate:
BMR = 10 × weight(kg) + 6.25 × height(cm) - 5 × age - 161The result is usually shown as calories per day. It is an estimate, not a precise measurement of your metabolism.
Worked example
Suppose a 35-year-old woman is 165cm tall and weighs 70kg. Using the Mifflin-St Jeor equation, the BMR estimate is around 1,395 calories per day.
10 × 70 = 700
6.25 × 165 = 1,031.25
5 × 35 = 175
700 + 1,031.25 - 175 - 161 = 1,395.25If she has light activity, the calorie calculator would multiply that BMR by an activity factor to estimate daily maintenance needs.
BMR vs TDEE
BMR is only the resting part of daily energy use. TDEE adds daily activity and exercise on top.
| Term | What it includes | How to use it |
|---|---|---|
| BMR | Estimated calories used at rest for basic body functions. | Useful as the base number inside a calorie calculation. |
| TDEE | BMR plus activity, exercise and daily movement. | Used to estimate maintenance calories. |
| Maintenance calories | The estimated calories needed to stay around the same weight. | Used before planning a deficit, surplus or macro split. |
What affects BMR?
- Body size: larger bodies generally need more energy at rest.
- Height and weight: these are core inputs in most BMR formulas.
- Age: BMR estimates usually fall with age in standard equations.
- Sex input: common equations use different constants for male and female estimates.
- Lean mass: muscle and organ mass can affect actual resting energy use, even when a formula cannot see the full picture.
- Health context: illness, medication, pregnancy, recovery and medical conditions can make generic estimates less suitable.
Limitations of BMR calculators
A BMR calculator is helpful for planning, but it is not a lab test. Formula results can be off for individuals, especially where body composition, health conditions or unusual activity patterns are involved.
For weight-change planning, a calorie deficit should be approached cautiously and sustainably rather than pushed to extremes.
Basal metabolic rate FAQs
Is BMR the same as maintenance calories?
No. BMR is the estimated energy used at rest. Maintenance calories include BMR plus daily activity and exercise.
Can I eat below my BMR?
A calculator cannot decide what is safe for you personally. Very low calorie intakes can be unsuitable or risky, so use professional guidance if you are unsure.
Does exercise change BMR?
Exercise affects total daily energy expenditure. It may also influence body composition over time, but the immediate extra calories from exercise are not part of BMR itself.
Why do different calculators give different BMR results?
Different calculators may use different formulas, activity multipliers or rounding rules. Treat the number as a planning estimate rather than an exact figure.
Sources and notes
- Mifflin-St Jeor resting energy equation paper: PubMed — A new predictive equation for resting energy expenditure
- NHS calorie guidance: NHS — understanding calories
- NHS Better Health calorie-counting guidance: NHS — calorie counting