There are ways to accurately smell your own breath. However you have to take a slightly indirect route.
Try this technique. Lick your wrist, wait about five seconds while the saliva dries somewhat, and then smell it. What do you think? That’s the way you smell. Or, more precisely, that’s the way the end of your tongue smells (your tongue’s “anterior” portion). How was it? Did you pass this first check?
Now try this experiment. It will check the odor associated with the back of your tongue (your tongue’s “posterior” aspect).
Take a spoon, turn it upside down, and use it to scrape the very back portion of your tongue. (Don’t be surprised if you find you have an active gag reflex.) Take a look at the material that has been scrapped off, usually it’s a thick whitish material. Now, take a whiff of it. Not so bad? Pretty nasty? This smell, as opposed to the sampling from the anterior portion of your tongue, is probably the way your breath smells to others.