BMR Calculator
Run the official BMR calculator any time your weight or routine changes.
Open BMR calculatorBasal metabolic rate explained
A practical walkthrough of the equations behind the BMR calculator and how to use them.
Basal metabolic rate (BMR) is the minimum energy your body needs to keep your heart beating, lungs breathing, and organs working while you rest. Getting this number right prevents you from underfueling or overestimating your maintenance calories.
This guide covers the formulas we support, how to gather accurate inputs, and the easiest way to pair BMR with activity so your nutrition plan stays realistic.
Ready to calculate?
Open the BMR calculator, apply these tips, and save your result so you can compare it with future check-ins.
Why BMR matters for every goal
BMR accounts for the biggest slice of your daily energy expenditure. Even if you skip the gym, your body spends calories to stay alive.
Understanding that baseline lets you layer activity on top without guesswork.
- BMR + activity = Total Daily Energy Expenditure (TDEE).
- RMR (Resting Metabolic Rate) is usually 1–3% higher than BMR because it is measured while you are awake.
- BMR shifts when weight, lean mass, or age change—track it over time.
Collect precise measurements
Age, sex, height, and weight drive the Mifflin-St Jeor equation. Adding body-fat percentage unlocks the Katch-McArdle formula that leans on lean mass.
Measure in the morning if possible and use consistent tools so your comparisons stay meaningful.
- Weigh yourself after using the restroom for a stable value.
- Measure height without shoes, standing tall against a wall.
- Update body-fat percentage monthly, or whenever your physique shifts.
Choosing between Mifflin-St Jeor and Katch-McArdle
Mifflin-St Jeor is validated across large populations and stays reliable even when body-fat data is unavailable.
Katch-McArdle uses lean mass. It reacts faster when your body composition changes, which is helpful for athletes or lifters with higher muscle mass.
- No body-fat number? Stick with Mifflin-St Jeor.
- Training with regular DEXA or caliper readings? Compare both results.
- If the formulas differ by more than 150 kcal, recheck your inputs.
Put your BMR to work
Use BMR as the anchor for deficit or surplus planning. Add activity through the TDEE or daily calories calculators to see how training changes the total.
Saving your numbers in the tracker helps you notice when metabolism adapts so you can adjust faster.
- Set maintenance targets with the TDEE calculator before you cut or bulk.
- Switch to the daily calculator on heavy training weeks to log steps and workouts.
- Recalculate BMR after every 5% weight change to keep macros aligned.
Quick checklist before you calculate
- Use consistent units (metric or imperial) for every input.
- Enter the most recent weight and measurements you trust.
- Decide which formula you will rely on and note it in your log.
Key terms to remember
These definitions match the labels inside the BMR calculator.
- BMR
- Basal Metabolic Rate—calories burned at complete rest.
- RMR
- Resting Metabolic Rate—similar to BMR but measured while awake and relaxed.
- Lean mass
- Your body weight minus fat mass. Katch-McArdle uses this to refine the estimate.
Pair your BMR with these calculators
Body-Fat Calculator
Need a lean-mass estimate? Use the body-fat calculator to refresh your percentage.
Measure body fatTDEE Calculator
Add activity multipliers with the TDEE calculator to see daily maintenance calories.
Estimate TDEEDaily Calories Calculator
Log steps and workouts in the daily calculator when you want a per-day breakdown.
Track daily burnMore energy guides
TDEE guide — turn BMR into maintenance calories
Learn how presets, NEAT, EAT, and TEF combine for realistic daily totals.
Read the TDEE guideDaily burn guide — plan deficit and surplus days
Break down training days versus rest days for smarter calorie cycling.
Read the daily burn guideSee also
BMR guide FAQ
Is there a difference between BMR and RMR?
They measure similar things. RMR is taken while you are awake and relaxed, so it can read slightly higher. Our calculator labels results so you know which equation produced them.
How often should I retest my BMR?
Recalculate after significant weight changes, body-fat updates, or when your routine shifts. Weekly checks help if you are dieting aggressively.
Do I adjust BMR when I start lifting weights?
Training itself does not change the formula, but gaining muscle raises lean mass. Update your body-fat percentage and rerun the numbers every few weeks.