April 18 was this year's deadline for most people to file their federal tax return and pay any tax they owe. If you are due a refund there is no penalty if you file a late tax return. If you owe tax, and you failed to file and pay on time, you will most likely owe interest and penalties on the tax you pay late. To keep interest and penalties to a minimum, you should file your tax return and pay the tax as soon as possible. Darrin T. Mish shares some facts that you should know.