A BMR calculator estimates how many calories your body burns at rest, before you add a single step of exercise or daily movement. That number is the foundation for setting a calorie target, whether the goal is losing weight, maintaining it, or eating enough to support training. This BMR calculator lets you pick the formula that matches the data you have, enter your basic stats, and see your resting burn alongside a full daily maintenance estimate.
How to use this BMR calculator
- Choose your units: metric (cm / kg) or imperial (in / lb).
- Select which formula to use: Mifflin-St Jeor, Harris-Benedict, or Katch-McArdle.
- Select your sex (male or female).
- Enter your age in years.
- Enter your height and weight in the units you chose.
- If you selected Katch-McArdle, enter your body fat percentage, since that formula calculates from lean body mass rather than total weight.
- Choose your activity level: sedentary, light, moderate, active, or very active.
- Click “Calculate metabolic rate” to see your results.
- Review the output: BMR in kcal per day, maintenance calories (TDEE), resting kcal per hour, BMR per kg of body weight, weekly maintenance, and the spread between formulas.
- Use “Copy report,” “Share,” or the PDF, Excel, and CSV export buttons to save or send your results, or click “Clear all” to start over.
What this BMR calculator does
The calculator takes your sex, age, height, and weight (plus body fat percentage if you choose Katch-McArdle) and runs them through the formula you select. The result is your basal metabolic rate: the calories your body needs just to keep organs, breathing, circulation, and cell repair running while you’re doing nothing else. From there, the calculator multiplies your BMR by an activity factor to estimate total daily energy expenditure, which is the calorie count most people actually use to plan a diet.
Because the tool supports three separate formulas, it also shows a formula spread, so you can see how much the estimate shifts depending on which equation you use. That spread is a useful reality check: no single BMR calculator output should be treated as an exact number, only as a starting estimate to refine over time based on how your weight actually responds.
BMR versus TDEE: two different numbers
BMR and TDEE answer different questions, and mixing them up is the most common mistake people make when setting calorie targets.
BMR: calories at complete rest
BMR reflects only the energy your body uses to stay alive with no activity at all, no digestion of food, no walking, no exercise. It’s a baseline, not a target to eat at.
TDEE: your real daily number
TDEE takes that baseline and adds back the calories burned through daily movement and exercise, using the activity multiplier you select. This calculator applies the following multipliers to convert BMR into TDEE.
| Activity level |
Description |
Multiplier |
| Sedentary |
Little to no exercise |
1.20 |
| Light |
Exercise 1 to 3 days a week |
1.375 |
| Moderate |
Exercise 3 to 5 days a week |
1.55 |
| Active |
Exercise 6 to 7 days a week |
1.725 |
| Very active |
Physical job plus regular training |
1.90 |
Choosing between the three formulas
Mifflin-St Jeor and Harris-Benedict both work from age, sex, height, and total weight, which makes them quick to use with information almost everyone already knows. Katch-McArdle instead calculates from lean body mass, so it needs a body fat percentage to run. If you know your body fat percentage from a scan or reliable measurement, Katch-McArdle can account for differences in muscle mass that weight-only formulas miss. If you don’t have that number, Mifflin-St Jeor or Harris-Benedict are the more practical starting point.
A note before you use your results
Every formula in this BMR calculator is built from population averages, so an individual result can run higher or lower than these equations predict, sometimes by 10 percent or more. Treat the BMR and TDEE figures as a starting point for planning, not an exact prescription. If you’re working toward a significant weight change, managing a medical condition, or training for a specific performance goal, check your plan with a doctor or registered dietitian. This tool is for general information and is not a substitute for medical advice.
Frequently asked questions
What is a good BMR calculator formula to start with?
Mifflin-St Jeor is a reasonable default because it only needs age, sex, height, and weight. Switch to Katch-McArdle if you have a reliable body fat percentage and want an estimate based on lean mass instead of total weight.
Should I eat at my BMR to lose weight?
No. Your BMR is the calorie amount your body burns at complete rest, not a daily eating target. Use the TDEE figure from the calculator as your baseline, then adjust it up or down depending on your goal.
Why do the three formulas give different results?
Each formula was built from different research populations and uses slightly different inputs, so they don’t converge on one identical number. The formula spread shown in the results reflects that natural variation, which is why this BMR calculator lets you compare all three.
How does the activity level affect my results?
The activity level you select applies a multiplier to your BMR to estimate TDEE, ranging from 1.20 for a sedentary lifestyle up to 1.90 for a physical job combined with regular training. Choosing an activity level that’s too high is a common reason people overestimate how much they can eat.
