BMR vs TDEE

On this page

1. Two numbers, two jobs
2. Is BMR a floor you shouldn’t eat below?
3. Planning a diet with both numbers
4. For athletes, the real floor is energy availability
5. How both numbers change as you lose weight
6. When your activity changes
7. If your measured TDEE comes out below your BMR
8. Questions about using BMR and TDEE

Two numbers, two jobs

People often ask which of the two numbers is “right”. Both are, because they answer different questions.

• BMR answers: how much energy does my body need just to run? It depends mostly on your size and how much lean tissue you carry.
• TDEE answers: how much do I burn on a normal day? It is BMR plus digestion, everyday movement and exercise, and it is the number your food should be planned around.

Our BMR vs TDEE comparison covers the definitions in detail. This guide is about using the two together to plan a diet that works and keeps working as you change.

Is BMR a floor you shouldn’t eat below?

You will often read that you must never eat below your BMR or your metabolism will “shut down”. That isn’t how the body works. There is no switch that flips at your BMR. A sedentary person eating slightly below their BMR may only be in a modest deficit, while their active friend eating exactly at BMR could be 35% short of what they burn.

What is true is that very large deficits cause problems: muscle loss, low energy, poor training, hunger that leads to rebound eating, and more adaptation in the long run. BMR is a handy sense check for that, especially if you are active:

• If your target is above your BMR, your deficit is almost certainly moderate.
• If you are active and your target is below your BMR, check the deficit as a percentage of TDEE. It is probably over 25%.
• Whatever the numbers, don’t go below about 1,200 kcal (women) or 1,500 kcal (men) a day without medical supervision, and aim to lose no more than about 1% of your body weight a week.

Planning a diet with both numbers

1. Work out your BMR and TDEE. Use the TDEE calculator, or the BMR calculator to compare four equations.
2. Set a target from TDEE. 15 to 25% below for fat loss, about the same for maintenance, 5 to 15% above for muscle gain.
3. Sense-check it against BMR and the calorie floors above.
4. Check the speed. Divide the daily deficit by 1,100 to get kilos a week (7,700 kcal per kilo ÷ 7 days), or by 500 for pounds.
5. Test it for two to four weeks and adjust from your weight trend.

Two examples:

A 36-year-old man, 176 cm (5′9″) and 88 kg (194 lb), who lifts four times a week:

BMR = 10 × 88 + 6.25 × 176 − 5 × 36 + 5 = 1,805 kcal TDEE = 1,805 × 1.55 = 2,798 kcal Target = 2,798 × 0.8 = 2,238 kcal (above his BMR: a moderate deficit) Speed = 560 ÷ 1,100 ≈ 0.5 kg (1.1 lb) a week

A 45-year-old woman, 162 cm (5′4″) and 70 kg (154 lb), with a desk job and little exercise:

BMR = 10 × 70 + 6.25 × 162 − 5 × 45 − 161 = 1,327 kcal TDEE = 1,327 × 1.2 = 1,592 kcal Target = 1,592 × 0.8 = 1,274 kcal (just under her BMR, still a 20% deficit) Speed = 318 ÷ 1,100 ≈ 0.3 kg (0.6 lb) a week

Her target sits just below her BMR, and that is fine: it is still only a 20% deficit, and it stays above 1,200 kcal. If she wanted more room, adding 3,000 daily steps would raise her TDEE by roughly 70 to 100 kcal and let her eat a little more for the same result.

For athletes, the real floor is energy availability

If you train hard, the useful “floor” isn’t your BMR at all. Sports scientists use energy availability: the calories left for the rest of your body after training has taken its share, expressed per kilo of fat-free mass.

Energy availability = (calories eaten − calories burned in training) ÷ fat-free mass (kg)

When it stays low for long, the body starts saving energy in ways that matter: periods become irregular or stop, bone health suffers, injuries and illness become more common, and performance falls. The International Olympic Committee calls this relative energy deficiency in sport, or REDs. A long-used rule of thumb from research in women is that energy availability below about 30 kcal per kilo of fat-free mass a day is a warning sign.

Here is how it plays out. A 60 kg (132 lb) runner with about 48 kg of fat-free mass eats 2,000 kcal a day and burns 700 kcal in training. Her energy availability is (2,000 − 700) ÷ 48 = 27 kcal per kilo, below that warning line, even though 2,000 kcal sounds like plenty and is well above her BMR. If you train a lot and your periods change, you feel run down or you keep getting injured, see a doctor or sports dietitian.

How both numbers change as you lose weight

A lighter body costs less to run, so both numbers fall as you lose. Here is the man from the example above, still lifting four times a week:

Each 5 kg lost trims about 50 kcal from his BMR and about 78 kcal from his TDEE. Eating the same amount, his deficit shrinks by more than 40% over 15 kg, so his weight loss slows even though nothing about his diet changed. That is not a broken metabolism; it is arithmetic.

On top of this, many people move a little less as they diet, and the body adapts slightly, so real TDEE often falls a bit faster than the table shows. The fix is simple: recalculate after every 4 to 5 kg (10 lb), or let your weigh-ins tell you. Our guide on why TDEE changes during weight loss explains the adaptation part.

When your activity changes

BMR barely moves when your routine changes. TDEE moves straight away. Typical examples:

• New desk job after a job on your feet: TDEE can drop by 300 to 600 kcal a day. Recalculate with a lower activity level before the scale tells you.
• Injury or illness: drop at least one activity level while you recover, but keep protein up to protect muscle.
• A new training block: if you go from three sessions a week to five, move up a level, then check after two weeks.

If your measured TDEE comes out below your BMR

When people track their food and weight, they sometimes calculate a TDEE that is lower than their estimated BMR. In a healthy adult living a normal day, that almost never reflects reality, because digestion and any movement at all add to resting burn. The usual explanations are:

• Food that didn’t get logged. In one well-known study, people who believed they couldn’t lose weight on low intakes were eating far more than they recorded. Oils, drinks and weekend meals are the common gaps.
• Water changes. The first week of a diet, a salty weekend or the days before a period can move the scale by a kilo or more.
• Too short a window. Two weeks is the minimum; three to four is better.

If you are confident your log is complete and your measured TDEE is still very low, it is worth asking your doctor to check for problems such as an underactive thyroid.

Questions about using BMR and TDEE

Can my TDEE be lower than my BMR?

Not in a healthy person living a normal day. TDEE is BMR plus digestion and movement, so it is always higher. If your tracking says otherwise, the usual reason is unlogged food or water changes, not your metabolism.

Is BMR the same as RMR?

Nearly. BMR is measured under strict lab conditions, after waking and fasting. RMR is measured under looser conditions and is usually a little higher. Calculators treat them as the same.

Why is my BMR so low?

Most often because of a smaller body or less muscle. Women usually have a lower BMR than men of the same weight, and it falls slightly with age. A health problem such as an underactive thyroid can also lower it.

Should I ever eat below my BMR?

If you are sedentary, a sensible deficit can land slightly below your BMR, and that is fine. If you are active, eating well below your BMR usually means a deficit of 30% or more, which is hard to sustain and costs muscle.

I train twice a day. How do I use BMR and TDEE?

Use the athlete level (×1.9) as a starting point and check your weight and energy every week. For you, the bigger risk is eating too little. Energy availability, the calories left after training, matters more than BMR.

How often should I update my BMR and TDEE?

After every 4 to 5 kg (10 lb) of weight change, and whenever your job or training changes. When your weight is stable, every few months is enough.

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