Health calculators

Mifflin St Jeor Calculator

Updated Sep 1, 2026 By Jehan Wadia
Rate Formulas Sources Medical disclaimer
Your Details
ages 15–80
Enter a whole number between 15 and 80.
Biological Sex
Please select your biological sex.
Enter a valid positive height.
Enter a valid positive weight.
Pick the option that best matches a typical week.
How Your BMR Was Calculated
Your BMR (Basal Metabolic Rate)
—
—
Calories your body burns at complete rest.
Your TDEE (Total Daily Energy)
—
—
—
Where You Fall in the Range
You
Sedentary
— Extra Active
—
Daily Energy Needs by Activity Level
Activity Level Description Calories/day
Exercise: 15–30 minutes of elevated heart rate activity.
Intense exercise: 45–120 minutes of elevated heart rate activity.
Very intense exercise: 2 or more hours of elevated heart rate activity.
Energy Needs Comparison
Supplementary: Body Mass Index
Your BMI: —
Healthy range: 18.5–24.9

Introduction

This Mifflin-St Jeor calculator helps you find out how many calories your body burns each day. It figures out two key numbers: your BMR (Basal Metabolic Rate) and your TDEE (Total Daily Energy Expenditure). Your BMR is the number of calories your body needs just to stay alive at rest: breathing, pumping blood, and keeping your brain working. Your TDEE takes your BMR and adds in the calories you burn through daily movement and exercise.

The Mifflin-St Jeor equation is one of the most accurate formulas for estimating calorie needs. It uses your age, height, weight, and biological sex to calculate your BMR. A systematic review found it predicts within 10% of measured metabolic rate in more people than any other common equation, with the narrowest error range.1

Knowing your TDEE is useful whether you want to lose weight, gain muscle, or maintain your current size. To lose weight, you eat fewer calories than your TDEE. To gain weight, you eat more. To stay the same, you match it. Enter your details below and pick your activity level. The calculator handles the rest, including a full step-by-step breakdown of the math.

How to Use Our Mifflin-St Jeor Calculator

Enter a few details about your body and activity level below. The calculator will show your BMR (calories burned at rest) and your TDEE (total calories burned per day).

Pick your unit system: Click "Imperial (US)" to use pounds and feet, or click "Metric" to use kilograms and centimeters.

Enter your age: Type your age in years. You must be between 15 and 80 years old to use this calculator.

Select your biological sex: Choose either Male or Female. The formula uses a different number for each sex to estimate your metabolism.

Enter your height: In Imperial mode, type your height in feet and inches. In Metric mode, type your height in centimeters.

Enter your weight: In Imperial mode, type your weight in pounds or switch to stones. In Metric mode, type your weight in kilograms.

Choose your activity level: Pick the option from the dropdown that best matches how much you exercise in a normal week. Options range from Sedentary (little or no exercise) to Extra Active (very intense daily exercise or a physical job).

Click "Calculate BMR & TDEE": Your results will appear below. You will see your BMR, your TDEE, a step-by-step breakdown of the math, a comparison table for all activity levels, a bar chart, and your BMI.

What Is the Mifflin-St Jeor Calculator?

This calculator uses the Mifflin-St Jeor equation to find out how many calories your body burns each day. It gives you two key numbers: your BMR and your TDEE.

What Is BMR?

BMR stands for Basal Metabolic Rate. It is the number of calories your body needs just to stay alive while doing nothing at all. Even when you sleep, your body uses energy to breathe, pump blood, and keep your organs working. Your BMR is that baseline energy cost. It does not include walking, eating, or any kind of movement. A closely related measure is your Resting Metabolic Rate.

What Is TDEE?

TDEE stands for Total Daily Energy Expenditure. It is the total number of calories you burn in a full day, including all your activity. Your TDEE takes your BMR and multiplies it by an activity factor based on how much you move and exercise during a typical week. If you want to maintain your current weight, you should eat roughly the same number of calories as your TDEE.

How the Mifflin-St Jeor Equation Works

The Mifflin-St Jeor equation was created by doctors M.D. Mifflin and S.T. St Jeor in 1990. It uses four inputs to estimate your BMR:

  • Weight in kilograms
  • Height in centimeters
  • Age in years
  • Biological sex (male or female)

The formulas are:

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

Most nutrition experts consider this equation the most accurate BMR formula for the general population. It replaced the older Harris-Benedict equation, which tends to overestimate calorie needs.

Why Your Activity Level Matters

Your BMR only covers rest. To get your true daily calorie needs, the calculator multiplies your BMR by an activity multiplier. Someone with a desk job who does not exercise will have a much lower TDEE than someone who trains hard six days a week. Picking the right activity level gives you a more useful and accurate result.

What You Can Do With Your Results

Once you know your TDEE, you can use it to guide your eating habits:

  • Maintain weight: Eat roughly the same calories as your TDEE.
  • Lose weight: Eat fewer calories than your TDEE. A common target is 500 calories below your TDEE per day, which works out to about one pound of fat loss per week.
  • Gain weight: Eat more calories than your TDEE.

These numbers are estimates. Things like genetics, muscle mass, hormones, and health conditions can all affect how many calories you truly burn. If you have specific health goals, talk to a doctor or registered dietitian for advice tailored to you.

Formulas used

BMR – Mifflin-St Jeor (Male)
\text{BMR} = (10 \times W) + (6.25 \times H) - (5 \times A) + 5
BMR – Mifflin-St Jeor (Female)
\text{BMR} = (10 \times W) + (6.25 \times H) - (5 \times A) - 161
Total Daily Energy Expenditure (TDEE)
\text{TDEE} = \text{BMR} \times \text{Activity Factor}
Body Mass Index (BMI)
\text{BMI} = \frac{W}{\left(\frac{H}{100}\right)^{2}}
Kilocalories to Kilojoules Conversion
E_{\text{kJ}} = E_{\text{kcal}} \times 4.184

Frequently asked questions

What is the difference between BMR and TDEE?

BMR is the calories your body burns doing nothing at all, just keeping you alive. TDEE is your BMR plus all the calories you burn from moving, exercising, and digesting food. Your TDEE is always higher than your BMR.

Should I eat my BMR or my TDEE to lose weight?

You should eat below your TDEE, not your BMR. Eating below your BMR for a long time can slow your metabolism and leave you without enough energy for basic body functions. A safe goal is to eat 500 calories less than your TDEE, which can lead to about one pound of weight loss per week.

How do I pick the right activity level?

Think about what a normal week looks like for you. If you sit most of the day and don't exercise, pick Sedentary. If you work out 3–4 times a week, pick Active. Be honest. Picking a level that is too high will give you a calorie number that is too high.

What is the difference between calories and kilocalories?

In everyday use, they mean the same thing. When food labels and this calculator say "calories," they actually mean kilocalories (kcal). One kilocalorie equals 1,000 small calories. You do not need to convert anything. Just use the number as shown.

What are kilojoules and when should I use them?

Kilojoules (kJ) are another way to measure energy. They are common in Australia, New Zealand, and parts of Europe. One calorie equals about 4.184 kilojoules. Click "Advanced Options" in the calculator and select kilojoules if that is the unit you prefer.

Why does BMR go down as I get older?

As you age, you tend to lose muscle mass and your cells slow down. Since muscle burns more calories than fat, less muscle means a lower BMR. The formula subtracts 5 calories for each year of age to reflect this natural decline.

How often should I recalculate my BMR and TDEE?

Recalculate whenever your weight, age, or activity level changes in a meaningful way. A good rule is to check every 4 to 6 weeks if you are actively trying to lose or gain weight. As your body changes, your calorie needs change too.

Is eating below my BMR dangerous?

Eating well below your BMR for a long time can be harmful. It may cause muscle loss, nutrient deficiencies, fatigue, and a slower metabolism. Your body needs at least your BMR worth of calories to keep organs and basic functions running properly.

Why is my TDEE so much higher than my BMR?

Your BMR only covers rest. Everything else you do (walking, working, exercising, even digesting food) burns extra calories. For active people, TDEE can be 1.5 to 1.9 times higher than BMR. The more you move, the bigger the gap.

What does the BMI number in the results mean?

BMI stands for Body Mass Index. It compares your weight to your height. A BMI between 18.5 and 24.9 is considered healthy for most adults. It is a quick screening tool, but it does not measure body fat directly and may not be accurate for athletes or very muscular people.

Sources

  1. Frankenfield D, Roth-Yousey L, Compher C. Comparison of predictive equations for resting metabolic rate in healthy nonobese and obese adults: a systematic review. Journal of the American Dietetic Association. 2005;105(5):775-789. doi:10.1016/j.jada.2005.02.005. Accessed September 1, 2026.

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