bmr calculator uk

What is BMR and why does it matter?

BMR stands for Basal Metabolic Rate. It is the number of calories your body needs each day to keep you alive at complete rest: breathing, circulation, temperature regulation, cell repair, and brain function. In simple terms, it is your baseline calorie requirement before walking, exercise, work, or household activity.

If you are in the UK and trying to lose fat, maintain weight, or build muscle, understanding BMR gives you a practical starting point. Instead of guessing calorie targets, you can estimate your needs and make small, measurable adjustments over time.

How this UK BMR calculator works

This page uses the Mifflin-St Jeor equation, one of the most commonly used formulas in nutrition practice. It estimates BMR from your sex, age, weight, and height. Then it applies an activity multiplier to estimate total daily energy expenditure (TDEE), which is your rough maintenance intake.

Step-by-step

• Enter your age and sex.
• Choose metric or UK/imperial units.
• Add height and weight accurately.
• Select activity level based on your real average week, not your best week.
• Review your BMR and estimated maintenance calories.

BMR vs TDEE vs BMI

BMR

Calories needed at complete rest.

TDEE (maintenance calories)

BMR multiplied by daily activity. This is usually the more practical number for meal planning.

BMI

A screening ratio of weight to height. Useful at population level, but not a full assessment of health or body composition.

Using your numbers for real goals

For fat loss

Start with a moderate calorie deficit (around 10% to 20% below maintenance). Aggressive cuts often reduce adherence and training quality. A slower, consistent approach usually works better over months.

For maintenance

Eat around your estimated TDEE and monitor your average body weight for 2 to 3 weeks. If weight drifts up or down, adjust intake by 100 to 200 kcal/day.

For muscle gain

Use a small surplus, often around 5% to 10% above maintenance, while prioritising resistance training and sufficient protein.

UK practical guidance

• Track trends, not single days. Water balance and sodium intake can shift scale weight quickly.
• Use kitchen scales where possible for better calorie accuracy.
• Account for weekend intake; many people undercount social meals.
• Use consistent weigh-ins (same time, same conditions).
• If you have a medical condition (thyroid disease, diabetes, eating disorder history), speak to your GP or registered dietitian before making major changes.

Formula used in this calculator

Mifflin-St Jeor Equation

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

The calculator then estimates maintenance calories by multiplying BMR by an activity factor (for example 1.2 to 1.9).

Limitations to keep in mind

Every calculator is an estimate. Your true energy needs can vary due to genetics, medications, hormonal changes, sleep, stress, menstrual cycle, lean body mass, and movement levels outside workouts.

The best method is: estimate, test for 2 to 4 weeks, then adjust based on outcomes.

Frequently asked questions

Is BMR the same as resting metabolic rate (RMR)?

They are close, but not identical. RMR is measured in less strict conditions and is usually slightly higher than true basal values.

Should I eat exactly my BMR calories?

Usually no. Most people should plan around TDEE (maintenance), then adjust up or down for goals.

How often should I recalculate?

Recalculate when body weight changes by roughly 2 to 4 kg, or when activity level changes significantly.

Can this calculator help with NHS weight management plans?

It can support awareness and planning, but it does not replace professional advice. For personalised care, use NHS services, your GP, or a registered nutrition professional.