As a general rule, the civil penalties found in the Internal Revenue Code are only equal to a ratio of the tax underpaid. So if you paid the tax in full there are generally no civil penalties. However, the general rule is subject to many exceptions where you can pay a penalty without owing tax (e.g. if you failed to comply with the foreign trust disclosure rules). I don't want to review every possible case where you can suffer a civil penalty without underpaying tax, but they do exist. I realise this isn't one of my most detailed posts, but it would be a lot of work to describe all of the potential penalties.