Do You Burn Calories While You Sleep?

The short answer

Yes, and almost exactly as much as lying still and awake. Sleep is the one activity that costs less than resting: the Compendium of Physical Activities lists it just below one metabolic equivalent. This page models the sleeping hour at 0.9 of resting rate, which is the convention used for the figures below.

At 75 kg that is about 64 kcal an hour, or 515 kcal across an eight hour night. It sounds like a lot until you notice that the same eight hours awake and resting cost about 573 kcal.

How the estimate is built

Everything starts from resting metabolic rate, which the BMR calculator gives from the Mifflin-St Jeor equation: 10 x weight in kilograms plus 6.25 x height in centimetres minus 5 x age, with a constant for sex.

Divide the daily resting figure by 24 to get the hourly cost, then scale it to sleep. At 75 kg the resting rate on this model is 1,718 kcal a day, so 72 kcal an hour awake and resting, and about 64 kcal an hour asleep at 0.9.

The same arithmetic in METs reaches the same place. One MET is close to 1 kcal per kilogram per hour, so a 75 kg adult at 0.9 MET spends about 67 kcal an hour. The two routes differ by a few percent, which is the honest precision of any number on this page.

Why the rate is not the same all night

Sleep is not one state. Deep slow wave sleep runs the metabolic rate below the nightly average, while REM sleep brings heart rate, breathing and brain activity back towards waking levels and can sit above it. Muscle relaxation removes most of the small cost of holding posture, which is where the saving against lying awake comes from.

The average is what matters for a daily total, and it lands near 0.9 of resting for a normal night. A night broken by long periods awake moves that average up towards the awake resting figure, because the awake hour is the more expensive of the two, which is one more reason the estimate is a model rather than a measurement.

Sleep is not exercise

A common claim is that a night of sleep burns as many calories as a workout. It does not. Eight hours asleep at 75 kg is 515 kcal, while a single hour of running at 9.8 MET costs about 772 kcal on the same model - half a night more than the whole night.

The related idea that you can sleep off a large meal is arithmetic against you: the dessert that cost 700 kcal takes roughly eleven hours of sleep to repay at 64 kcal an hour. Sleeping well is worth doing for its own reasons, not as a training session.

Sleep debt and the next day's eating

Short sleep does not change the cost of the hours you do sleep by much. What it changes is the following day. Controlled studies that restrict sleep in healthy adults consistently report higher hunger and higher energy intake, with the extra calories tending to arrive as snacks rather than at meals.

Set against the small change in overnight expenditure, a few hundred extra calories eaten is the larger effect by an order of magnitude. That is the honest reason sleep belongs in a weight conversation: not because of what the night burns, but because of what the following day eats.

The direction of that finding is consistent across studies; the exact size of the effect is not, and it varies with how severe the restriction is and how long it lasts. Treat it as a reason to protect sleep, not a number to plan with.

What changes the number, and what does not

A large meal raises expenditure for a few hours through the thermic effect of food, but the effect fades before deep sleep and is small next to the meal's own calories. A cold bedroom raises energy use slightly, because the body defends its core temperature, and that increase is real if modest.

Adding muscle changes the resting rate by roughly 10 to 15 kcal per kilogram of tissue per day, so three kilograms of hard-won muscle is worth about 40 kcal a day. Genuine, slow, and unrelated to how well you sleep tonight. Nothing about the sleeping hour itself is directly trainable.

None of that is an argument against sleeping cold or eating late if you like it. It is an argument against expecting either habit to move the daily total much in one direction or the other.

Why a watch or a sleep app disagrees

Sleep trackers estimate energy from heart rate, movement and time asleep, then apply a model much like the one above. Their advantage is knowing when you were actually asleep; their weakness is that wrist movement is a rough proxy for sleep stages and that heart rate falls for reasons other than metabolic rate.

Treat the tracker and this page as two estimates of the same thing. A disagreement of ten percent is the models talking, not evidence that one of them is broken.

How to use the number

The nightly figure is most useful as a reminder of scale. Sleep accounts for roughly a quarter of a day's energy expenditure and does so whether the night was good or bad. To see where the rest goes, the BMR calculator gives the resting baseline and the TDEE calculator multiplies it by an activity level.

For weight change the deficit calculator is the one that matters. Better sleep will not create a deficit by itself, and no amount of arithmetic about the night changes the fact that the daytime decisions set the total.

The nightly figure is also a useful check on the fasting advice that circulates around sleep. Eating in a short window changes when calories arrive, not what the night itself costs, and the calculator takes no view on either.

Frequently asked questions