According to the Internal Revenue Service (IRS) instructions, the penalty for late filing of Form 1120S is generally $205 for each month or part of a month the return is late, multiplied by the total number of shareholders in the S corporation during any part of the corporation's tax year (up to a maximum of 12 months). The penalty can be waived if the S corporation can show "reasonable cause" for the late filing, but the IRS has the final authority to determine whether reasonable cause exists. It is important to note that penalties and instructions may vary, so it is recommended to consult the official IRS instructions or a tax professional for the most accurate and up-to-date information.