Did you claim every tax break that you were entitled to when you filed your 2009 federal tax return this year? Now that the pressure is off and the April 15 deadline for filing your return has passed, it may be worth your time to give your return a thorough review. There were so many new tax breaks for 2009 that it would have been easy to miss a few. If you did, you may have received a smaller refund – or paid a bigger tax bill – than you should have. But you can set things right by filing an amended tax return now, which could put more money in your pocket in a matter of months.

Don't worry if you discover a simple math error, though. You don't need to file an amended return. The IRS can correct computation errors and will send you a notice if you owe more money or are entitled to a bigger refund.

Missing forms
Sometimes, the IRS will accept returns that are missing certain forms or schedules. For example, many taxpayers were confused by the new Schedule M used to claim the Making Work Pay credit – a 6.2% payroll tax credit worth up to $400 for individuals or $800 for married couples. (The Making Work Pay tax credit is phased out for high earners starting at $75,000 for single taxpayers and $150,000 for couples filing a joint return.)

Although most employees received the credit throughout the year in the form of lower tax withholding, you had to file Schedule M to claim the credit and adjust your tax bill accordingly. Retirees who received a $250 economic-recovery check or direct deposit in the summer of 2009 and who had earned income from a job in 2009 are also required to file a Schedule M. To avoid prohibited double dipping, retirees must deduct the $250 payment they received from the $400 Making Work Pay credit for a net tax credit of $150.

But the new Schedule M caused lots of confusion, and millions of people who should have filed one didn't. So the IRS took matters into its own hands. "Most of the time, we're going to pick up that omission," says Eric Smith, a spokesman for the IRS. "Normally, we'll send you a math-error notice showing the adjustment." If your refund is larger than you expected, it means the IRS computed the proper tax for you and included the credit amount in your refund. (Retirees with earned income who failed to subtract their $250 economic-recovery check may get a smaller refund than expected.) If you didn't claim the Making Work Pay credit and the IRS didn't adjust your refund, file an amended return to claim your extra cash.

Another new form – Schedule L – also caused some confusion. On this form, taxpayers who didn't itemize their deductions could claim an enhanced standard deduction for net disaster losses, sales or excise tax paid on the purchase of a new car after February 16, 2009, and a property-tax deduction of up to $500 ($1,000 for married couples filing jointly). If you missed one of those tax breaks, file an amended return.

Don't wait to claim the home buyer's credit
Another case in which you may want to file an amended return: You bought a new house in 2010 and qualify for either the $8,000 first-time home buyer's credit or the $6,500 credit for longtime residents who bought another principal residence. You don't have to wait until you file your 2010 tax return to claim it. Special rules allow you to claim it on your 2009 return as long as you signed a binding contract before May 1, 2010, and close on the home before July 1. Amend your 2009 return by filing Form 1040X. (You'll also have to file Form 5405, "First-Time Homebuyer Credit and Repayment of the Credit," and include a copy of your settlement sheet.)

Review education credits
There were so many new tax breaks to offset the cost of college tuition that it's possible you didn't claim the best one for your situation. Say you have a child who attended college as a freshman or sophomore last year in one of the seven midwestern states that were declared federal disaster areas following the devastating spring floods of 2008. (The affected states are Arkansas, Illinois, Indiana, Iowa, Missouri, Nebraska and Wisconsin, but not all counties in every state qualify.)

Depending on your income, you could claim the supercharged Hope credit for the midwestern disaster area, with a top credit of $3,600 for qualified students, rather than the $2,500 American Opportunity credit available to students elsewhere in the country. Caution: If you choose the Hope credit, you cannot claim the American Opportunity credit for any student in the same year. And while a portion of the American Opportunity credit is refundable if you owe no tax, the Hope credit is not. Tax-preparation software can help you figure out which tax break is best for your situation.

Check your filing status
Perhaps you are single and normally use the tax-rate tables for single individuals to compute your tax. But your daughter and grandchild moved in with you last year, and now you realize that you should have filed as head of household to take advantage of more-generous tax rates and claim the $1,000 child tax credit for your dependent grandchild. File an amended return.

Above-the-line deductions
Or maybe you're accustomed to filing a simple return using Form 1040EZ and didn't know that there are several tax breaks you can claim even if you didn't itemize your tax deductions. You need to use the right form. For example, non-itemizers can deduct up to $2,500 of interest paid on student loans and contributions to an IRA. Teachers and other educators can deduct up to $250 in out-of-pocket expenses for classroom supplies. You can claim the deductions on either Form 1040 or 1040A. If you moved to take a new job, you may be able to deduct your moving expenses on Form 1040. If you missed any of these tax so-called above-the-line deductions, file an amended return.

Mail your paperwork
Generally, you have three years from the date of your original return or two years from the date you paid the tax, whichever is later, to claim a refund. (You have seven years to amend a bad debt or loss incurred in that tax year.) Fill out Form 1040X, which you can download at www.irs.gov. Enter the corrected numbers and explain why you need to amend your original tax form. You don't have to redo your entire return; just make the necessary changes and adjust your tax liability accordingly.

Unlike your regular income-tax return, you can't file Form 1040X electronically. You can prepare it electronically but you'll have to print it out and mail it to the IRS. Figure it will take about 12 weeks to process your request. And you can't ask for direct deposit, either. The IRS will mail your refund check to you. If you are filing amended tax returns for several different years, mail each amended return in a separate envelope. You may also need to file an amended return with your state tax agency.

Reprinted with permission. All Contents © 2010 The Kiplinger Washington Editors. www.kiplinger.com