For myself, that answer seems to be about 500 calories.

That's assuming I sleep for about eight hours, and get a deep sleep with dreams.

I stand at 5'8" tall and weigh between 150-160 pounds. The larger the person you are, the more calories are burned sleeping. The calories burned remains proportional to weight, thus a 300 pound person would get double the calories burned that I get, about 1,000. A 200 pound person would be about 625 calories burned.

If you have a lot of muscle-mass, you'll burn even more calories during sleeping, compared to a similar-weight person with average muscle-mass. This is because your body has to feed energy to those muscles; the more muscles you have, the more calories it burns to fuel them. Likewise, the more energy you expended that day, the more calories it burns to replenish those muscles.

Sleep is when the body grows most of its new cells. If you suffered some damaged tissues, such as a cut, a bruise, a strain or a sprain, the body will grow cells to repair those tissues. And that requires burning more calories too.

You can also burn more calories if you are sleeping through cool or cold temperatures (as your body has to burn calories to create heat).

So, you can factor that into your overall weight loss plan as you count calories consumed and calories burned.