Hello I have a client that owed $200,000 at extension time 2022 and did not have the funds to pay the tax. We extended his return. Come October 15 2023, he only had $40,000 to pay and was still missing some info so he paid in $40,000 at that time. We could not file his return until January 2024 when the IRS efile system cam back up. On the penalty to file does it start after the extension date and is the unpaid balance the penalty is assessed on the $200,000 or should it only be on the $160,000, after his payment? He did not pay in 90% of the taxes he owed by 4-15-23.

Thank You

Steve A.