Why do I owe taxes? I claimed what I should have!?

My husband and I made a little over $60,000 and only claimed 2 exemptions throughout the whole year. We're just claiming standard deductions since we don't own a home and have no kids. The online tax program is saying that I'm going to owe almost $800 for the feds and over $300 for the state. How is this possible when we only claimed what we should have?????????