April 15 is the final day for US taxpayers to file their income tax returns with the Internal Revenue Service (IRS). Taxpayers needing more time can request an extension until October 15, but they must pay any taxes owed by today to avoid penalties. The IRS warns that mailing delays could hinder timely filing, advising taxpayers to file online or obtain a hand-stamped postmark if mailing their forms. Failure to file on time results in penalties starting at 5% of unpaid taxes each month, reaching a maximum of 25%. If a return is over 60 days late, a minimum penalty of either $525 or 100% of the tax owed applies. Additionally, interest on unpaid taxes compounds daily, currently at a rate of 7%. However, there are no penalties for late filing if no taxes are owed or if a refund is due, highlighting the importance of timely submissions for those expecting refunds.