How to Calculate Your BMR (Basal Metabolic Rate) Accurately

Guides · Calculator · Updated 2026

Your Basal Metabolic Rate (BMR) is the number of calories your body burns at complete rest — just to keep your heart beating, lungs breathing, and cells functioning. Knowing it is the foundation of any weight loss, gain, or maintenance plan. Toolzo’s free BMR Calculator uses the Mifflin‑St Jeor equation, the most accurate formula for the general population. This guide explains the formula, shows a worked example, and clarifies the difference between BMR and BMI.

BMR vs. BMI: what’s the difference?

BMR is about calories (energy), while BMI (Body Mass Index) is a simple ratio of weight to height used to categorise underweight, normal, overweight, or obese. BMR gives you actionable dietary data; BMI is a screening tool. You can calculate your BMI with our BMI Calculator, but for a personalised calorie target, BMR is the key. After calculating BMR, you multiply it by an activity factor to get Total Daily Energy Expenditure (TDEE).

Set accurate daily calorie goals.
Understand why two people of the same weight might need different calories.
Track metabolic changes as you age or change body composition.

The Mifflin‑St Jeor BMR formula

      For men: BMR = (10 × weight in kg) + (6.25 × height in cm) − (5 × age) + 5

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

Worked example

A 30‑year‑old woman weighing 65 kg and 165 cm tall:

BMR = (10 × 65) + (6.25 × 165) − (5 × 30) − 161 = 650 + 1031.25 − 150 − 161 = 1,370.25 calories/day

If she’s moderately active (factor 1.55), her TDEE is 1,370 × 1.55 ≈ 2,124 calories/day. The calculator does this automatically.

Step‑by‑step: use the BMR calculator

Open the BMR Calculator tool.
Enter your age, select gender, and fill in weight (kg) and height (cm).
Click “Calculate”. Your BMR is displayed, along with a table showing daily calories for five activity levels — from sedentary to very active.

💡 Tip: Use the “very active” category only if you have a physically demanding job or train intensely for hours daily. Overestimating activity leads to eating too many calories.

Using BMR for weight goals

To lose weight, create a deficit of about 500 calories per day below your TDEE. To gain, add a surplus. Our BMR calculator gives you the starting numbers. If you also want to track body composition, the BMI Calculator provides a quick snapshot, though BMR is more personalised. For fitness tracking, combine BMR data with the Pomodoro Timer to manage study or workout sessions.

Frequently Asked Questions

Why does BMR decrease with age?

As we age, muscle mass tends to decrease and fat mass increases, which lowers the metabolic rate.

Can I use pounds and inches?

The calculator uses kg and cm; you can convert pounds and inches using our Weight Converter first.

Is the Mifflin‑St Jeor formula the best?

It’s widely considered the most accurate for the general population without advanced lab equipment.

Does BMR include exercise calories?

No, BMR is for resting energy. The activity multipliers estimate total daily needs.

Is the tool free?

Yes, completely free and private.

Try the BMR Calculator