Dogs like having their bellies rubbed. They happily flop on their backs, tongue lolling and tail wagging as they await tummy scratches. But why?
Why do dogs like their bellies rubbed so much?

Dogs expose their bellies to us for two main reasons: as a submissive display, and as a request for a belly rub. It’s important to know what your dog is telling you before you go in for petting!
Submissive Behaviour vs. Wanting Belly Rub
Dogs adopting a submissive display (also called an appeasement display) are trying to diffuse social tension by showing that they’re not a threat. Petting a dog who’s showing submissive or appeasing behaviours can make the dog more nervous because now you’re touching him in very vulnerable parts of his body!
Dogs who actually want a belly rub will generally show the following body language signals:
Loose, wiggly body postures
Relaxed, open mouth – you might see their tongue flopping around
Open or squinty eyes, bright and not necessarily staring at anything
Relaxed, wagging tail
In contrast, a dog who is showing submissive or appeasing behaviour will look like this:
Tense, low body postures – they may crouch, freeze, or tense up
Mouth: lips pulled far back in a fear grimace or lips and mouth closed, may see lots of lip-licking and tongue-flicking
Eyes: wide open and staring into the distance, or showing the whites of their eyes as they look at you, without turning their head, or eyes will be squinty and tense
Tail: may be still or wagging, but will have tension in the base of the tail and the tail may be tucked
Quiet or soft whining
Most people find it easiest to watch the dog’s tail and mouth – but keep in mind that a wagging tail doesn’t always mean a happy dog. A tucked, stiff, fast tail wag is not the same as a full-body, loose tail wag!
It’s hard to say exactly why dogs love belly rubs—we can’t ask our pets! Since dogs can’t easily scratch their own tummies, they’re more likely to rely on humans for help.
Many dogs also enjoy rolling in carpet or grass to really itch their backs. Anecdotally, it seems that many dogs seem to enjoy getting a belly rub while they also scratch their backs. They can reach their own shoulders, necks, and face with their hind feet. But they really don’t have a good way to scratch their own tummies!
Think of how nice it feels to have someone rub your back or scratch an itch that you can’t reach. No wonder dogs love getting a helping hand with their belly rubs!
The most important thing is to respect your dog’s wishes and pet him the way he’d like to be petted. If you listen to your dog’s body language, you will make your dog love belly rubs even more than he already does!