Calculator
What the BMR Calculator does
BMR Calculator: calculates BMR (kcal / day) from Your Weight, Your Height and Your Age. Formula: Mifflin-St Jeor: BMR = 10 x weight(kg) + 6.25 x height(cm) - 5 x age + s. Example: your weight 70 kg, your height 170 cm and your age 30 years gives BMR (kcal / day) 1,617.5.
Point it at Your Weight, Your Height, Your Age and Sex and it returns BMR (kcal / day). Results refresh instantly, so trying variations costs nothing but a moment.
A single number is most useful as a trend over time rather than a one-off judgement. That is usually what brings someone starting a new plan here.
Your data stays on your machine. Once the page has loaded you could disconnect entirely and it would still work.
The sections that follow cover the fields, the method, and one full example computed from the defaults.
What do the BMR Calculator fields mean?
The BMR Calculator uses 4 inputs. Every field is populated on load; treat those numbers as a template rather than a suggestion.
| Field | What to enter | Default |
|---|---|---|
| Your Weight | measured in kg | 70 |
| Your Height | measured in cm | 170 |
| Your Age | measured in years | 30 |
| Sex | choose from Male or Female | Male |
How does the BMR Calculator work?
s is +5 for men and -161 for women. Multiply BMR by an activity factor to estimate daily energy needs.
Nothing is computed until the inputs pass their checks, so you will not get a confident answer built on a typo.
Worked example
These are the values the BMR Calculator loads by default, and the result it produces from them. This walkthrough uses the starting values, which means you can follow along without typing anything.
| Your Weight | 70 kg |
|---|---|
| Your Height | 170 cm |
| Your Age | 30 years |
| Sex | Male |
| BMR (kcal / day) | 1,617.5 |
|---|---|
| What this means | About 1618 kcal/day keeps basic body functions going at rest (breathing, organs). Daily needs are higher once you… |
Which equation this uses, and why it matters
This uses the Mifflin-St Jeor equation, which predicts resting energy expenditure from weight, height, age and sex. It replaced Harris-Benedict as the default because it was more accurate in the populations it was validated against, but every such equation is a population average applied to an individual.
Worth knowing
- BMR is what you would burn at complete rest. It is not a calorie target: nobody spends the day at rest, and eating at BMR is a substantial deficit for almost everyone.
- Mifflin-St Jeor predicts resting expenditure within roughly 10% for most people, which on a 1,600 kcal BMR is a band of about 160 kcal. Treat the output as the middle of a range, not a precise figure.
- The equation takes no account of body composition. Two people of identical weight, height, age and sex but very different muscle mass get the same answer, and the more muscular one is under-predicted. Where body-fat percentage is known, the Katch-McArdle equation uses lean mass instead and is usually the better choice.
- Sex is an input because the original data differed by sex, largely as a proxy for average differences in lean mass. It is a statistical adjustment, not a statement about any individual.
Sources: Mifflin MD et al., Am J Clin Nutr 1990 (PMID 2305711) · WHO: healthy lifestyle recommendations
Read next: BMR and TDEE: Why Every Calculator Gives You a Different Number
How to use it
- Enter Your Weight in kg.
- Set Your Height in cm.
- Put Your Age in years.
- Pick a value for Sex: the options are Male or Female.
- Because it recalculates as you type, you can dial a value in rather than guessing and re-running.
- You get BMR (kcal / day) and What this means back.
- Share the link rather than a screenshot. It carries the values with it.
What this tool does not do
- Body composition, ethnicity and age all shift what a "normal" result means.
- These formulas come from population averages and cannot account for your medical history.
- It cannot flag an input that is technically valid but wrong for your case.
- Results are only as good as the inputs. Check your units before reading anything into the output.
Frequently asked questions
Enter Your Weight in kg, Your Height in cm and Your Age in years. Look for the unit beside each label; the result is reported in a stated unit as well.
With the values loaded when the page opens, BMR (kcal / day) comes out as 1,617.5. Change a value and the number is recomputed on the spot.
It is not stored or transmitted. The calculation happens locally and leaves no trace with us.
It is free to use, with no premium tier holding back the useful parts.
The arithmetic is correct; the model is a population approximation. Individual factors move the real answer, so treat the figure as context rather than a conclusion.