BMR Calculator (UK)
Calculate the calories your body burns at rest using the Harris–Benedict equation. Plan a deficit or surplus from your true baseline.
Basal Metabolic Rate (BMR) Explained
Basal Metabolic Rate (BMR) is the minimum number of calories your body requires to perform basic life-sustaining functions at rest. This includes breathing, circulating blood, cellular production, nutrient processing, and temperature regulation.
BMR accounts for approximately 60% to 75% of your total daily calorie burn. It is calculated using formulas like the Harris-Benedict equation or the Mifflin-St Jeor equation, which factor in age, biological sex, weight, and height. Because muscle tissue requires more energy than fat tissue at rest, increasing your lean muscle mass will elevate your BMR over time.
Knowing your BMR helps you determine your metabolic baseline. You should never consume fewer calories than your BMR for extended periods unless under strict medical supervision, as doing so can trigger metabolic slowdown, nutrient deficiencies, and muscle loss.
Frequently Asked Questions
Q: What is BMR?
BMR stands for Basal Metabolic Rate, representing the energy your body expends just to stay alive at rest, without any activity or food digestion factored in.
Q: Does eating below BMR damage metabolism?
Consuming calories below your BMR for too long can cause adaptive thermogenesis (metabolic slowdown) where your body conserves energy and burns muscle for fuel.
Medically reviewed by Dr. Rekha Kumar, M.D., M.S. — Lead Medical Reviewer · Last reviewed: September 2026 · Updated: 2026-09-15
Evidence & references
This tool is for informational purposes only and is not a substitute for professional medical advice.
Frequently asked questions
Is this calculator free to use?
Yes. Every calculator on Weight Loss Percentage is free, with no sign-up or account required.
How accurate is the result?
Results depend on the accuracy of what you enter and the published formulas the tool uses, which follow standard guidance from national health authorities. Track the trend over weeks rather than relying on a single reading.
How often should I check it?
Check whenever your weight, activity or goals change — for most people once a week is enough to see a reliable trend.
Who reviews the content on this site?
All medical and nutrition content is written and reviewed by Dr. Rekha Kumar, M.D., M.S., our lead medical reviewer, and cites guidance from U.S. federal health sources such as the CDC and NIH.