By Sarah Bolton
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September 9, 2025
September 15 Individuals: Pay the third installment of 2025 estimated taxes (Form 1040-ES), if not paying income tax through withholding or not paying sufficient income tax through withholding. Calendar-year corporations: Pay the third installment of 2025 estimated income taxes, completing Form 1120-W for the corporation’s records. Calendar-year S corporations: File a 2024 income tax return (Form 1120-S) and provide each shareholder with a copy of Schedule K-1 (Form 1120S) or a substitute Schedule K-1 if an automatic six-month extension was filed. Pay any tax, interest and penalties due. Calendar-year S corporations: Make contributions for 2024 to certain employer-sponsored retirement plans if an automatic six-month extension was filed. Calendar-year partnerships: File a 2024 income tax return (Form 1065 or Form 1065-B) and provide each partner with a copy of Schedule K1 (Form 1065) or a substitute Schedule K1 if an automatic six-month extension was filed. Employers: Deposit Social Security, Medicare and withheld income taxes for August if the monthly deposit rule applies. Employers: Deposit nonpayroll withheld income tax for August if the monthly deposit rule applies. September 30 Calendar-year trusts and estates: File a 2024 income tax return (Form 1041) if an automatic five-and-a-half-month extension was filed. Pay any tax, interest and penalties due. October 10 Individuals: Report September tip income of $20 or more to employers (Form 4070).