Filing tax returns is one of the most important financial tasks of the year, and if you are distracted during the filing process, you could make mistakes. Any lapse in the filing process can make you miss out on larger refund claims and make you pay additional tax. Further, errors in the paperwork can result in added interest, penalties, and audits from the Internal Revenue Service. So here are tax filing mistakes to avoid: Missing deadlines The most common tax filing mistake to avoid is missing the return filing deadline. This can mean a 5% penalty on the amount due for each month or each partial month the return is delayed. The maximum penalty is capped at 25% of the total due amount. If you are about to miss the deadline, you can request an extension by filing Form 4868 before the tax-filing deadline, and you will receive more time to complete the paperwork. Incorrect Social Security Number Social Security Numbers are used by the IRS to cross-reference information collected from an employee against that received from the employer, bank, and other establishments. So accidentally typing an incorrect SSN can disrupt the process and result in a rejection of returns.