BMR and TDEE explained

The two numbers worth knowing before you start

Search for diet advice and you quickly run into abbreviations like BMR and TDEE. The names sound technical, but the ideas are simple. Once you know these two numbers, the question "how much should I actually eat?" has an answer you can reason about instead of guess at.

What basal metabolic rate (BMR) is

Your basal metabolic rate is the energy your body burns doing nothing at all — lying in bed for a full day. It covers your heartbeat, your breathing, keeping your body temperature stable, and running your brain.

For most people this is the largest single share of daily energy use, usually 60–70%. In other words, you burn far more calories simply being alive than you do exercising. That is also why very aggressive dieting backfires: if your BMR falls, you end up needing less food than before just to hold your weight.

How to calculate it

Several formulas exist, but the most widely used today is the Mifflin-St Jeor equation. Published in 1990, it has held up well against measured values in later research, and it is treated as a default in most calculators and clinical settings.

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

Take a 30-year-old woman, 163cm, 58kg:

(10 × 58) + (6.25 × 163) − (5 × 30) − 161 = 580 + 1018.75 − 150 − 161 = about 1,288kcal

So even spending the entire day in bed, she would burn roughly 1,288kcal.

What total daily energy expenditure (TDEE) is

Nobody actually spends the day in bed. You commute, climb stairs, wash dishes, maybe train. Digesting food costs energy too.

Add all of that on top and you get your TDEE — the total calories you burn in a day. It is estimated simply, by multiplying BMR by an activity factor.

TDEE = BMR × activity factor

Choosing an activity factor

This is the number people most often overestimate. If you hit the gym three times a week but sit for the rest of your waking hours, 1.375 is closer to reality than 1.55. When the scale does not move the way your maths predicted, dropping one activity level is the first thing to try.

Continuing the example above, a moderately active person with a BMR of 1,288kcal has a TDEE of 1,288 × 1.55 = about 1,996kcal.

Turning TDEE into a target

TDEE is the number that keeps your current weight. Adjust from there:

• Weight loss: subtract 300–500kcal
• Maintenance: leave it as is
• Weight gain: add 300–500kcal

Losing 1kg of body fat requires roughly a 7,700kcal deficit. At 500kcal a day, that works out to about 0.45kg a week in theory. The calculator on this site applies a 500kcal adjustment when you pick a loss or gain goal.

How to read the result

Everything above produces an estimate. Two people of identical height, weight and age can have different real metabolic rates depending on how much muscle they carry, and the formula has no way to account for that. If you have trained for years, your true expenditure is likely higher than the number you get.

Treat it as a starting point. Hold that intake for two to three weeks, track your weight, and if nothing moves, adjust in steps of about 200kcal.

One safety note: diets below roughly 1,200kcal for women and 1,500kcal for men carry a real risk of nutrient shortfall and are not generally recommended. If your calculated target lands below that, increasing activity is safer than cutting food further.

This article is general information and is not a substitute for medical advice. If you have a health condition or take medication, speak with a professional before changing your diet.