Third Quarter The third quarter of a calendar year is made up of July, August, and September. July 15 Social security, Medicare, and withheld income tax. If the monthly deposit rule applies, deposit the tax for payments in June. Nonpayroll withholding. If the monthly deposit rule applies, deposit the tax for payments in June. August 2 Social security, Medicare, and withheld income tax. File Form 941 for the second quarter of 2010. Deposit or pay any undeposited tax under the accuracy of deposit rules. If your tax liability is less than $2,500, you can pay it in full with a timely filed return. If you deposited the tax for the quarter in full and on time, you have until August 10 to file the return. Certain small employers. Deposit any undeposited tax if your tax liability is $2,500 or more for 2010 but less than $2,500 for the second quarter. Federal unemployment tax. Deposit the tax owed through June if more than $500. All employers. If you maintain an employee benefit plan, such as a pension, profit-sharing, or stock bonus plan, file Form 5500 or 5500-EZ for calendar year 2009. If you use a fiscal year as your plan year, file the form by the last day of the seventh month after the plan year ends. August 10 Social security, Medicare, and withheld income tax. File Form 941 for the second quarter of 2010. This due date applies only if you deposited the tax for the quarter in full and on time. August 16 Social security, Medicare, and withheld income tax. If the monthly deposit rule applies, deposit the tax for payments in July. Nonpayroll withholding. If the monthly deposit rule applies, deposit the tax for payments in July. September 15 Social security, Medicare, and withheld income tax. If the monthly deposit rule applies, deposit the tax for payments in August. Nonpayroll withholding. If the monthly deposit rule applies, deposit the tax for payments in August. Third Quarter The third quarter of a calendar year is made up of July, August, and September. July 12 Employees who work for tips. If you received $20 or more in tips during June, report them to your employer. You can use Form 4070. August 10 Employees who work for tips. If you received $20 or more in tips during July, report them to your employer. You can use Form 4070. September 10 Employees who work for tips. If you received $20 or more in tips during August, report them to your employer. You can use Form 4070. September 15 Individuals. Make a payment of your 2010 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 2010. For more information, see Publication 505 . Corporations. File a 2009 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 2009 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 2009 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. Corporations. Deposit the third installment of estimated income tax for 2010. A worksheet, Form 1120-W, is available to help you estimate your tax for the year. The information in this tax calendar was copied from the Internal Revenue Service Publication 509.