This bill, the Tax Administration Simplification Act, aims to modernize federal tax administration by extending the "mailbox rule" to electronic submissions and simplifying S corporation compliance. It stipulates that the date an item is electronically sent will be deemed the official date of delivery or payment, regardless of when the IRS receives it, applying to submissions after December 31, 2025. Additionally, the legislation grants the Secretary of the Treasury authority to treat both late S corporation elections and revocations as timely if there was reasonable cause for the delay, offering greater flexibility for businesses. Furthermore, the bill adjusts the due dates for the second and third quarterly estimated income tax payments for individuals. The second payment is moved from June 15 to July 15 , and the third payment from September 15 to October 15 . These changes will apply to installments due in taxable years beginning after December 31, 2025, providing individuals with more time for these specific payments.