My toilet fills up and shuts off then the bowl empties what's wrong?

The most likely cause is a crack in the interior of the toilet. It is also possible that a plugged vent is forcing the system to vent through the toilet. Fill the toilet and then flush another toilet. What happens to the water level? Does it stay the same or "burp" and pull the water out? If it does that, you probably have a plugged vent. If it just slowly trickles away, you most likely have a cracked toilet.

Hi Jessealburton...

As unlikely as it is you could have a small crack in the toilet bowl or even a manufacturer's repair plug could have loosened somewhere in the trapway/bowl as suggested by ma0641...

Could also be the vent issue he suggested as well... ;) You will certainly want to check as described and let us know what you find.

Another issue that can cause this to happen is if something gets caught up in the toilet trapway or at the outlet of the toilet and it just hangs there and SIPHONS the bowl to almost empty. Here, tampons, paper towels, mop rags, heck, even dental floss can do it if enough gets hung up... ;) For this, you would try using a CLOSET AUGER tool and see if that frees or catches the stuff causing the issue, or you would have to lift the toilet and examine the toilet outlet and the waste pipe inlet.

To tell you much more, please describe how quickly the toilet bowl is evacuating after the bowl is filled. Is it almost instant, or is there a small or large delay before the bowl empties? Let us know more, OK?

Mark