Yes, late filing penalties will apply. If you filed for extension before 03/15/2024, your late filing penalties will apply from 09/15/2024. If you did not file for extension, late filing penalties will apply from 03/15/2024. In any case, try to file your return as soon as possible to avoid further penalties.
IRS charges a penalty if an S corporation or partnership tax return is filed after the deadline. The penalty is $235 for each person who was a shareholder or partner at any time during the tax year, for each month or part of a month that the return was filed late, for up to 12 months.
Look at page number 7 of this pdf link for penalties: https://www.irs.gov/pub/irs-pdf/i1065.pdf
