Calorie (BMR) calculator

This calculator estimates how many calories your body burns in a day, so you can see roughly how much to eat to stay at your current weight. It starts from your resting metabolism and then accounts for how active you are.

What BMR actually measures

Your basal metabolic rate (BMR) is the energy your body uses at complete rest — keeping your heart beating, your lungs moving air, your kidneys filtering, and your temperature steady. It is the floor of your daily burn, the cost of simply staying alive for 24 hours without moving. For most adults it accounts for roughly 60 to 70 percent of all the calories they use in a day, which is why it is the sensible place to start any calorie plan.

We use the Mifflin-St Jeor equation, published in 1990 and now the formula most dietitians reach for because it tracks modern bodies more closely than the older Harris-Benedict equation. It is plain arithmetic:

• Men: (10 × weight in kg) + (6.25 × height in cm) − (5 × age) + 5
• Women: (10 × weight in kg) + (6.25 × height in cm) − (5 × age) − 161

Take a 30-year-old man at 80 kg and 180 cm. The equation gives 800 + 1,125 − 150 + 5 = 1,780 calories a day at rest. A 35-year-old woman at 65 kg and 165 cm works out to 650 + 1,031 − 175 − 161, or about 1,345 calories. The 166-calorie sex term is not bias; it reflects that, on average, women carry a higher share of body fat, which is less metabolically demanding than muscle.

From BMR to TDEE: the activity factor

BMR alone is not what you eat to. Add walking, working, training, and even fidgeting and you get your total daily energy expenditure (TDEE) — the maintenance number this calculator reports. We reach it by multiplying BMR by a standard activity factor:

• Sedentary (1.2) — desk job, little deliberate exercise
• Light (1.375) — light exercise one to three days a week
• Moderate (1.55) — moderate exercise three to five days a week
• Active (1.725) — hard exercise six or seven days a week
• Very active (1.9) — physical job or twice-daily training

The multiplier matters more than most people expect. That same 1,780-calorie man maintains on about 2,136 calories if sedentary, 2,759 if moderately active, and 3,382 if very active. The gap between sitting all day and training hard is over 1,200 calories — more than a full meal. Choosing the level that honestly matches a typical week is the single biggest factor in getting a useful number, so when in doubt, pick the lower option.

Using the number to lose, gain, or hold

The figure shown is your maintenance level. To change weight, you shift away from it:

• To lose weight, eat below maintenance. A deficit of roughly 500 calories a day tends to produce about a pound of fat loss a week, since a pound of body fat stores around 3,500 calories.
• To gain weight, eat above it — a surplus of 250 to 500 calories supports a steady gain while limiting how much of it is fat.
• To hold steady, aim for the maintenance figure and let your weight confirm it over a few weeks.

Cutting too aggressively backfires: very low intakes are hard to sustain and can cost you muscle. A modest, consistent gap almost always beats an extreme one.

Why your number drifts over time

BMR is not fixed. Age alone moves it — the same 80 kg, 180 cm man burns about 1,780 calories at rest at 30 but closer to 1,680 at 50, because the equation subtracts five calories for every year. Losing weight lowers it too, since a smaller body costs less to run, which is part of why weight loss tends to slow. Recheck your number whenever your weight shifts by several pounds or your routine changes, and treat the result as a well-grounded starting point rather than a fixed quota: real metabolisms vary by 5 to 10 percent in either direction, so let a few weeks on the scale fine-tune it.

Frequently asked questions

Last reviewed June 2026. Calories are estimated with the Mifflin-St Jeor equation. For general guidance, not medical advice.