About the BMR Calculator
BMR Calculator helps estimate the key numbers involved in fitness decisions. It is designed for quick scenario comparison: enter a realistic set of values, calculate the result, then change one assumption at a time to see what has the greatest effect. Unlike a static table, the result responds to your inputs and keeps the calculation in your browser. Health and fitness results are population-based estimates. They can support a conversation or planning process, but they do not determine an individual diagnosis, treatment, or safe activity level.
How to use this calculator
Enter values that match your situation and select Calculate result. Review the main result and its supporting figures, then change one input at a time to compare scenarios. Results are rounded for readability while the calculation retains additional precision internally.
Information you will need
- Age
- Sex
- Weight
- Height
- Activity
- Body Fat %
- Formula
How the calculation works
Estimates BMR using Mifflin-St Jeor, Harris-Benedict, or Katch-McArdle (requires body fat %). TDEE = BMR x activity multiplier. Read the primary result together with the supporting values rather than focusing on one number alone. A useful estimate should make its assumptions visible. If the answer looks surprising, verify the unit, rate, time period, and whether the entered value is gross or net. Run a conservative and an optimistic scenario to understand the range of possible outcomes.
Formula or method
Mifflin: 10W + 6.25H - 5A + 5 (male) or -161 (female). Harris-Benedict: Classic equation. Katch-McArdle: 370 + 21.6 × lean body mass.
Worked example
Maintenance calories at moderate activity.
The example is illustrative rather than a recommendation. Use your own verified values and keep all monetary or measurement units consistent. When comparing alternatives, save or note each result so the assumptions do not become mixed.
How to interpret the result
The primary output answers the main question posed by the bmr calculator, while the additional cards provide context. A result with many decimal places is not necessarily more certain. The displayed precision makes comparison easier, but uncertainty in the inputs can be larger than the rounding difference.
Look for trends and ranges instead of treating a single estimate as a pass or fail result. If the output conflicts with symptoms, professional advice, or a direct measurement, rely on appropriate professional assessment.
Limitations and important notes
The bmr calculator cannot account for every factor that affects an individual result. Measurement technique, hydration, body composition, medication, pregnancy, illness, training status, and normal biological variation may matter. Do not use an estimate to diagnose a condition, select medication dosage, decide whether to drive, or ignore symptoms. A qualified professional can interpret measurements in the context of history and appropriate testing.
Frequently asked questions
What is BMR?
BMR (Basal Metabolic Rate) is the number of calories your body burns at complete rest to maintain basic functions like breathing, circulation, and cell production. It represents roughly 60–70% of your total daily calorie burn. Your BMR is the baseline that activity and digestion build on. Knowing it helps you understand how many calories you need before any exercise is added to the equation.
How do I calculate my BMR?
This calculator uses the Mifflin-St Jeor equation, widely considered the most accurate for healthy adults. Men: BMR = 10W + 6.25H − 5A + 5. Women: BMR = 10W + 6.25H − 5A − 161, where W is weight in kg, H is height in cm, and A is age in years. The result is an estimate, and your actual BMR measured in a lab can differ by a few hundred calories.
Does building muscle increase BMR?
Yes, modestly. Muscle is metabolically active, so more lean mass means a somewhat higher resting burn. That said, the effect is often overstated — adding a few pounds of muscle raises BMR by maybe 20–50 calories a day. Resistance training's bigger value is improving body composition and daily energy expenditure. This calculator assumes an average body composition; a very muscular build can raise true BMR above the estimate.
Why does BMR decrease with age?
BMR declines roughly 2–3% per decade after young adulthood, mostly because muscle mass tends to shrink while fat increases, and metabolic rate per unit of tissue falls slightly. Hormonal changes also play a role. This is why the Mifflin-St Jeor equation includes age. Strength training and adequate protein can slow the muscle loss that drives much of the decline, but some change is a normal part of aging.
What is the difference between BMR and RMR?
BMR is measured under strict conditions — fasted, fully rested, in a warm room — and represents the energy needed just to stay alive. RMR (resting metabolic rate) is slightly higher and easier to measure, since it does not require the same overnight fasting and rest. Both reflect your baseline calorie burn, and this calculator's estimate sits between the two. The difference is small enough to ignore for practical purposes.
How can I raise my BMR?
The most reliable levers are building and keeping muscle, staying consistently active, and avoiding crash dieting, which can lower your resting burn. Adequate protein and sleep help support muscle and metabolic health. Be realistic: changes from diet and training are modest, often a few dozen calories per day from muscle gain. The calculator's estimate is a useful baseline; your doctor or dietitian can help you interpret it.
Why is my BMR lower than my partner's?
BMR is driven by body size, muscle mass, age, and sex. Men generally have more muscle and larger frames, so their BMR runs higher than women's on average. A bigger or more muscular person of either sex will also burn more at rest. Genetics causes further variation. Differences of a few hundred calories are common and normal — the estimate matters most as your own personal baseline, not as a comparison.