Individuals – Make a payment of your estimated tax for 2010 if you did not pay your income tax for the year through withholding (or did not pay in enough tax that way). Use Form 1040-ES. This is the final installment date for 2010 estimated tax. However, you do not have to make this payment if you file your 2010 return (Form 1040) and pay any tax due by January 31, 2011.

Employers – Nonpayroll Withholding. If the monthly deposit rule applies, deposit the tax for payments in December 2010.

Farmers and Fishermen – Pay your estimated tax for 2010 using Form 1040-ES. You have until April 18 to file your 2010 income tax return (Form 1040). If you do not pay your estimated tax by January 18, you must file your 2010 return and pay any tax due by February 28, 2011, to avoid an estimated tax penalty.

Businesses – Give annual information statements to recipients of 1099 payments made during 2010.

Employers – Federal unemployment tax. File Form 940 for 2010. If your undeposited tax is $500 or less, you can either pay it with your return or deposit it. If it is more than $500, you must deposit it. However, if you already deposited the tax for the year in full and on time, you have until February 10 to file the return.

Employers – Social Security, Medicare, and withheld income tax. File Form 941 for the fourth quarter of 2010. Deposit any undeposited tax. (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 February 10 to file the return.

Employers – Nonpayroll taxes. File Form 945 to report income tax withheld for 2010 on all nonpayroll items, including backup withholding and withholding on pensions, annuities, IRAs, gambling winnings, and payments of Indian gaming profits to tribal members. Deposit any undeposited tax. (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 year in full and on time, you have until February 10 to file the return.

Individuals – who must make estimated tax payments. If you did not pay your last installment of estimated tax by January 18, you may choose (but are not required) to file your income tax return (Form 1040) for 2010. Filing your return and paying any tax due by January 31 prevents any penalty for late payment of last installment.

Payers of Gambling Winnings – If you either paid reportable gambling winnings or withheld income tax from gambling winnings, give the winners their copies of Form W-2G.

Certain Small Employers – File Form 944 to report Social Security and Medicare taxes and withheld income tax for 2010. Deposit or pay any undeposited tax under the accuracy of deposit rules. If your tax liability is $2,500 or more from 2010 but less than $2,500 for the fourth quarter, deposit any undeposited tax or pay it in full with a timely filed return.

Electing Large Partnerships – File a 2009 calendar-year return (Form 1065-B). This due date applies only if you were given an additional 6-month extension. See March 15 for the due date for furnishing the Schedules K-1 to the partners.

Employers (nonpayroll withholding) – If the monthly deposit rule applies, deposit the tax for payments in September.

Employers (Social Security, Medicare, and withheld income tax) – If the monthly deposit rule applies, deposit the tax for payments in September.