Depending on your physique, you might see abs but carry more weight in your bottom half. You can try an electronic fat measurement, like a scale or hand-held device that sends a current through you.
I wouldn't EVER depend on something on the computer for an accurate reading.
The two most realistic are the calipers test (done by someone who is not you) and the water-submerging test.
Women usually (read: usually does not apply to everyone) develop a stomach "line" between 18-20 percent.