TDEE vs BMR: How Many Calories Do You Actually Need Each Day?

If you've ever looked into calorie tracking, you've probably run into two acronyms almost immediately: BMR and TDEE. They sound similar and get used somewhat interchangeably online, but they measure two genuinely different things, and mixing them up is one of the easiest ways to end up eating far too little or far too much. Here's what each one actually means, the formula behind them, and a worked example to show how they fit together.

What is BMR?

BMR, or Basal Metabolic Rate, is the number of calories your body burns just to keep you alive if you did absolutely nothing all day: no walking, no talking, no digesting food, just lying still and breathing. It covers things like keeping your heart beating, your organs functioning and your body temperature stable. For most adults, BMR accounts for the majority of total daily calorie burn, often somewhere between 50% and 75%, even though it only reflects being completely at rest.

What is TDEE?

TDEE, or Total Daily Energy Expenditure, is your BMR plus everything else your body burns in a normal day: walking around, working, exercising, digesting food, and even small movements like fidgeting. TDEE is the number that actually matters if you're trying to maintain, lose or gain weight, since it reflects your real day-to-day calorie needs rather than just your resting baseline.

The Mifflin-St Jeor formula

The most widely used formula for estimating BMR today is Mifflin-St Jeor, published in 1990 and generally considered more accurate for the modern adult population than the older Harris-Benedict equation from 1919. It uses your weight, height, age and sex:

The formula gives an estimate in calories per day. From there, TDEE is calculated by multiplying your BMR by an activity multiplier that reflects how much you move day to day.

Activity level multipliers

The standard activity multipliers used alongside Mifflin-St Jeor are based on how much structured exercise and general movement you do in a typical week, in line with the pattern the NHS uses when describing physical activity levels for adults.

Worked example

Take a 35-year-old woman who weighs 70kg and is 165cm tall, and does moderate exercise three to five days a week.

BMR = (10 × 70) + (6.25 × 165) − (5 × 35) − 161 = 700 + 1,031.25 − 175 − 161 = 1,395 calories a day, just to maintain basic bodily functions at rest.

TDEE = 1,395 × 1.55 (moderately active multiplier) = 2,163 calories a day, her estimated maintenance calories once her activity level is factored in.

That's a difference of 768 calories a day between BMR and TDEE, purely down to movement and activity, which shows why using BMR alone as a target for eating or weight management would significantly underestimate what most people actually need.

Why the difference matters

Confusing BMR and TDEE is one of the most common calorie-counting mistakes. Someone who eats to their BMR figure, rather than their higher TDEE figure, is creating a much bigger calorie deficit than they realise, which can leave them undereating, low on energy and more likely to lose muscle along with fat. On the other end, someone who overestimates their activity level and inflates their TDEE multiplier can end up eating more than they think and stall their progress without understanding why. Getting an accurate starting estimate for both numbers, then adjusting based on how your actual weight changes over a few weeks, is a far more reliable approach than guessing.

Limitations to keep in mind

• These are estimates, not measurements. Mifflin-St Jeor is a population-average formula; your individual metabolism could reasonably sit 10-15% either side of the number it gives you.
• Body composition isn't factored in. Muscle burns more calories at rest than fat does, so the formula can underestimate BMR for very muscular people and overestimate it for people with a higher body fat percentage.
• Activity level is self-reported. It's easy to overestimate how active you really are; tracking your actual weight change over two to three weeks against your intake is the most reliable way to calibrate your real TDEE.
• This isn't medical advice. If you have a health condition affecting your metabolism, or any concerns about your weight or eating, speak to your GP rather than relying on a calorie formula alone.

Once you know your TDEE, you might also want to check a healthy weight range with our BMI Calculator, work out a target weight with the Ideal Weight Calculator, or see your BMR on its own with the BMR Calculator. For more on healthy weight ranges generally, see our UK BMI guide.

Frequently asked questions