Here are the most common mistakes the IRS sees from self-prepared returns: (1) Math errors – be sure to check your math twice; (2) Misspelled name or changed name not updated (be sure the name on the return matches the name on your W-2); (3) Entering an incorrect Social Security number; (4) Incorrect direct deposit information for refunds (routing and account numbers); (5) failing to update any changes in filing status; (6) trying to take a charitable contribution deduction for a non-501(c)(3) organization; (7) forgetting to sign or date the return; (8) forgetting or neglecting to send in your return by April 15.