You did not specify if the extension you filed was for Federal or for a state. However, by filing an extension you have until 10/15/2024 to get your taxes filed. Filing an extension gives you that extra time to file your returns; however, an extension does not give you extra time to pay a balance due. Please see the following link for more information on penalties and interest: https://www.irs.gov/taxtopics/tc653
My apologies. I thought you were referring to the penalties for the filing deadline for individual tax returns. To answer your question, the penalty for filing your S-Corp business return after Sept 15th is $235. for each month or part of a month (up to 12 months) the return is late, multiplied by the number of shareholders or partners.