March 16

Corporations. File a 2008 calendar-year income tax return (Form 1120 or      1120-A) and pay any tax due. You can apply for an automatic six-month extension with Form 7004. If you file for an extension, you must also make an estimated tax payment.

S corporations. File a 2008 calendar-year tax return (Form 1120S) and pay any tax due. Send each shareholder a copy of Schedule K-1 (Form 1120S) or a substitute Schedule K-1. You can apply for an automatic six-month extension with Form 7004, but you must pay any tax due.

S corporation election. File Form 2553 to choose to be treated as an S corporation beginning with calendar year 2009. If Form 2553 is filed late, S treatment will begin with calendar year 2010.

Electing large partnerships. Provide each partner with a copy of Schedule K-1 (Form 1065-B). This due date is effective for the first March 15 following the close  of the partnership's tax year and applies even if the partnership seeks an extension of time.

April 15

Tax return due. Your 2008 income tax return is due, unless you file for an extension until Oct. 15.

File for extension. If you want an automatic extension of time to file your 2008   tax return, file Form 4868. Filing the form gives you until Oct. 15 to file your return. To avoid a penalty, however, be sure to pay any tax that was due on April 15.

Individual Retirement Accounts or Roth IRAs. This is the deadline for    making contributions to IRAs or Roth IRAs for tax year 2008.

Estimated tax payment. Your first-quarter estimated tax payment for 2009 is  due.

State tax returns. If you are required to file a state tax return, it is probably     due -- but check with your state to be certain. Many states automatically extend    the filing time for those who have filed for a federal extension.

Household employers. If you paid cash wages of $1,500 or more in 2008 to a household employee, file Schedule H (Form 1040) with your income tax return and report any employment taxes by April 15.

June 15

Filing deadline. If you're a U.S. citizen or resident alien living and working (or on military duty) outside the U.S. and Puerto Rico, file Form 1040 and pay any tax, interest and penalties due. You can file for an extension until Oct. 15.

Estimated taxes due. Your second-quarter estimated tax payment (using Form 1040-ES) for 2009 is due.

Sept. 15

Estimated tax due. Your third-quarter estimated tax payment (using Form 1040-ES) for 2009 is due.

Oct. 15

Income tax return due. Your 2008 income tax return is due if you filed an extension request using Form 4868.

Dec. 31

Deduction deadline. The last date to make payments that can be deducted from your 2009 return.

Keogh plan deadline. The last date to establish a Keogh plan so you can deduct    a Keogh plan contribution on your 2009 return.