September – Federal Specific

September 15

Employers: Social security, Medicare, and withheld income tax. If the monthly deposit rule applies, deposit the tax for payments in August.

Non-payroll withholding: If the monthly deposit rule applies, deposit the tax for payments in August.

Individuals: Make a payment of your present year estimated tax if you are not paying your income tax for the year through withholding (or will not pay in enough tax that way). Use Form 1040-ES. This is the third installment date for estimated tax in the present year.

Corporations: File a last calendar year income tax return (Form 1120) and pay any tax, interest, and penalties due. This due date applies only if you timely requested an automatic 6-month extension. Otherwise, see March 15.

S-corporations: File a last calendar year income tax return (Form 1120S) and pay any tax due. This due date applies only if you timely requested an automatic 6-month extension. Otherwise, see March 15. Provide each shareholder with a copy of Schedule K-1 (Form 1120S) or a substitute Schedule K-1.

Partnerships: File a last calendar year return (Form 1065). This due date applies only if you were given an additional 5-month extension. Provide each partner with a copy of Schedule K-1 (Form 1065) or a substitute Schedule K-1.

September – State Specific

Resellers: File and pay state sales taxes you have collected as obliged by the California State Board of Equalization (BOE) on the date of this month that BOE has designated for you.

September 15

Individuals: Third-quarter estimated tax due for present year (Form 540-ES)

September – County Specific

September – City Specific