If you didn’t file your 2017 taxes in April, Monday is your extension deadline. Lifehacker reports failing to file your taxes by Monday will result in a five percent monthly failure-to-file penalty fine if you owe money to the IRS. The penalty will continue to stack up each month, up to 25 percent. There are a few circumstances under which you might qualify for an additional extension, including if you were affected by Hurricane Florence and, likely, Hurricane Michael.