BMR is the energy your body uses just to keep you alive: heart, brain, breathing, temperature. It's the single biggest piece of what you burn each day — but it is not a calorie target.
Your basal metabolic rate is the floor of your energy needs. Most adults sit somewhere between 1,300 and 1,900 kcal, and BMR typically makes up around 60–75% of everything you burn in a day. The rest comes from movement and digestion.
Don't eat at your BMR to lose weight. This is the most common mistake: people see a BMR of 1,600 and eat 1,600, not realising that ignores every calorie they burn walking, working, and exercising. That creates a far larger deficit than intended. Your real target comes from TDEE, not BMR.
This calculator offers Mifflin-St Jeor (the modern default, most accurate for the general population), Revised Harris-Benedict (an older but still-used equation), and Katch-McArdle (the most accurate if you know your body-fat percentage, because it works from lean mass). Switch between them in the formula dropdown above.
No. BMR is what you burn at complete rest. TDEE is BMR multiplied by an activity factor, and represents your total daily burn including movement and digestion. Use TDEE, not BMR, to set calorie targets.
For most people without a body-fat measurement, Mifflin-St Jeor is considered the most accurate. If you know your body-fat percentage, Katch-McArdle can be more precise because it uses lean body mass.
No. Eating below BMR for extended periods can drive muscle loss and other problems. A moderate deficit from your TDEE is the safer approach — this site never sets a target below your BMR.