BMR Calculator
Estimate the calories your body burns at rest each day using the Mifflin-St Jeor equation.
Example
For a 30-year-old male, 175 cm tall, weighing 70 kg:
BMR = 10(70) + 6.25(175) - 5(30) + 5
= 700 + 1093.75 - 150 + 5
= 1648.75
≈ 1,649 kcal/day
For a female with the same stats, replace +5 with -161, giving about 1,483 kcal/day.
How it works
Enter your sex, age, height (cm), and weight (kg). The calculator applies the Mifflin-St Jeor formula to estimate your resting daily energy expenditure.
Good to know
This BMR Calculator estimates your basal metabolic rate—the number of calories your body burns in a full day of complete rest just to keep core functions like breathing, circulation, and cell repair running. You enter four metrics (sex, age, height in centimeters, and weight in kilograms) and it applies the Mifflin-St Jeor equation, recalculating instantly as you type. It's aimed at anyone setting a calorie target for weight loss, maintenance, or gain who wants a credible starting baseline rather than a guessed number.
The result panel gives you more than a single figure. Alongside your daily BMR in kcal, it breaks the number down per hour and pre-multiplies it by two common activity factors: x1.2 for a sedentary lifestyle and x1.55 for moderate activity. Read these as rough maintenance-calorie brackets: eat consistently below the bracket that matches your routine and you tend to lose weight over time; eat above it and you tend to gain. Your true expenditure usually sits somewhere across that range depending on how much you actually move.
A few specifics worth knowing about this particular tool. It is metric-only—heights are in cm and weights in kg, so convert before entering (1 inch is 2.54 cm; 1 lb is about 0.4536 kg). It uses biological sex as a binary input because the equation only has a male/female constant (+5 versus -161), and it floors any impossible negative result at zero. Because Mifflin-St Jeor relies on total body weight, it can overestimate BMR for very muscular people and underestimate it for those with higher body fat, since it cannot see body composition.
Treat the output as a planning estimate, not a precise measurement—real BMR is measured in a lab via indirect calorimetry and can vary by 5 to 15 percent from any formula. A practical tip: pick the activity multiplier closest to your week, eat at that level for two to three weeks, and adjust by 100 to 200 kcal based on how your weight actually trends rather than re-running the math repeatedly.
Frequently asked questions
What is the Mifflin-St Jeor equation?
It is a widely used formula for estimating BMR: 10 x weight(kg) + 6.25 x height(cm) - 5 x age + 5 for men, or - 161 for women. It is considered more accurate for modern populations than the older Harris-Benedict equation.
Is BMR the same as daily calorie needs?
No. BMR is the calories burned at complete rest. Your total daily needs (TDEE) are higher because they include activity. Multiply BMR by an activity factor (about 1.2 sedentary to 1.9 very active) to estimate maintenance calories.
Is my data uploaded anywhere?
No — this calculator runs entirely in your browser; nothing is uploaded.
Is this a substitute for medical advice?
No. These are educational estimates — consult a qualified health professional for medical decisions.
People also ask
What is a normal BMR for my age and weight?
There is no single normal number because BMR scales with sex, age, height, and body mass. As rough context, many adult women fall around 1,200 to 1,500 kcal/day and many adult men around 1,500 to 1,900 kcal/day, but the calculator gives a figure tailored to your exact inputs.
Why does my BMR go down as I get older?
In the Mifflin-St Jeor equation, every year of age subtracts 5 kcal from the estimate, reflecting the general decline in resting metabolism with age. Loss of lean muscle mass over time is one of the main physiological reasons this happens.
How accurate is the Mifflin-St Jeor BMR formula?
Studies generally find it predicts measured resting energy expenditure within about 10 percent for most healthy adults, which is why it is widely preferred over older equations. Accuracy drops for people at extremes of body composition, such as very lean athletes or those with obesity.
Should I eat at my BMR to lose weight?
BMR represents calories burned at complete rest, so eating only at that level while also being active typically creates a large deficit. Most calorie targets are based on total daily expenditure (BMR times an activity factor) minus a moderate deficit, rather than on BMR alone.
What is the difference between BMR and RMR?
BMR is measured under strict conditions—fully rested, fasted, and at a comfortable temperature—while resting metabolic rate (RMR) is measured under less restrictive conditions and runs slightly higher. The two terms are often used interchangeably, and the difference is usually only a few percent.
Does muscle mass increase BMR?
Yes, lean muscle is more metabolically active at rest than fat, so people with more muscle tend to have higher resting energy expenditure. The Mifflin-St Jeor equation uses only total weight, so it cannot directly account for how much of that weight is muscle versus fat.
How do I convert pounds and inches for this calculator?
This tool uses kilograms and centimeters only. Divide your weight in pounds by 2.2046 to get kilograms, and multiply your height in inches by 2.54 to get centimeters before entering the values.
Can BMR change day to day?
Resting metabolism can fluctuate modestly with factors like sleep, illness, hormones, recent food intake, and temperature. The calculator gives a stable estimate from your body metrics and does not capture these short-term variations.
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