By now, everyone knows something about the home buyer tax credit. But here s a detail that may have escaped you. You can claim a credit on your 2009 return for a home purchased this year. However, taking that action may or may not be advisable for you, and there are some procedural issues if you decide to go for it. Here s the story.

Last November, Congress passed legislation to extend the home buyer credit to cover purchases that close by April 30, 2010. The credit is also available for purchases that are still under contract as of that date, as long as they close by June 30, 2010.

If you re a so-called first-time home buyer, the credit is equal to the the lesser of: (1) $8,000, or (2) 10% of the purchase price, or (3) $4,000, if you re married but file separately from your spouse.

Being a first-time home buyer means you did not own a U.S. principal residence during the three-year period ending on the purchase date for the home that will serve as your new principal residence. If you re married, both you and your spouse must pass this three-year test (even if you file separate returns). To clarify, if you (or your spouse) previously owned a home but have not owned one in the last three years, you re still eligible for the first-time home buyer credit. (So it s a misnomer.)

Bottom Line: The maximum credit for so-called first-time buyers is $8,000, and it can be claimed for 2010 purchases that close by the magic dates.

Existing homeowners can benefit

The November legislation also established a new but less-generous credit for so-called longtime homeowners who close on a U.S. principal residence after Nov. 6, 2009, and before April 30, 2010. If the home is under contract as of that date, the closing deadline is extended to June 30, 2010.

The new longtime homeowner credit is equal to the lesser of: (1) $6,500, or (2) 10% of the purchase price, or (3) $3,250, if you use married filing separate status.

To qualify for this deal, you must have owned and used the same home as your principal residence for at least five consecutive years during the eight-year period ending on the date you purchase a new principal residence. If you re married, both you and your spouse must pass this five-out-of-eight years test (even if you file separate returns).

Bottom Line: The maximum credit for so-called longtime homeowners is $6,500, and it can be claimed for 2010 purchases that close by the magic dates.

Higher-income buyers are eligible, too

The familiar first-time home buyer credit and the new longtime homeowner credit are phased out (reduced or completely eliminated) as your income rises. However, the November legislation significantly raised the phase-out ranges for purchases that close after Nov. 6, 2009, including purchases that close in 2010 by the magic dates. As a result, many more higher-income buyers can qualify for credits under the current liberalized phase-out ranges.

* The current phase-out range for unmarried individuals and married folks who file separately is between modified adjusted gross income (MAGI) of $125,000 and $145,000.

* The current phase-out range for married joint filers is between MAGI of $225,000 and $245,000.

* MAGI is the adjusted gross income figure reported on the last line on the first page of your Form 1040 increased by certain types of tax-exempt income from sources outside the U.S., which only a few buyers will have.

Bottom Line: The liberalized MAGI phase-out ranges apply to 2010 purchases that close by the magic dates.

Claim a 2009 credit for a 2010 purchase

So, here s what you need to understand about the option of claiming a first-time home buyer credit or a longtime homeowner credit from a 2010 purchase on your 2009 Form 1040.

First, timing is everything. Claiming your rightful credit sooner rather than later could be advantageous for two reasons.

1. You ll get the tax-saving benefit much quicker if you claim the credit on your 2009 return, rather than waiting to claim it on your 2010 return, which won t be filed until sometime next year.

2. Because of the MAGI phase-out rule, you might qualify for a bigger credit if your 2009 income was lower than what you expect it to be this year. However, be careful because the opposite could also happen. If you expect this year s income to be lower, claiming the credit on last year s return could be a bad idea if the phase-out rule would result in a lower credit. The good news: the current liberalized MAGI phase-out ranges apply to a 2010 purchase even if you claim the resulting credit on your 2009 return.

Claiming the credit on your 2009 return also involves following some new procedures. You must complete and attach the updated version of Form 5405 (First-Time Homebuyer Credit), which says Rev. December 2009 at the top. For most purchases, the updated form requires you to attach a properly executed real estate settlement sheet (typically a HUD-1 form). If you purchase a manufactured home and don t get a settlement sheet, you must attach an executed retail sales contract. If you have a new home built just for you and don t get a settlement sheet, you must attach a certificate of occupancy. Additional documentation is required if you claim the new longtime homeowner credit or if your purchase closes between May 1, 2010 and June 30, 2010.

Note that you can only claim a home buyer credit if your 2009 Form 1040 is on paper. Electronic filing is not allowed because of the aforementioned documentation requirements.

Finally, please take my advice and extend your 2009 Form 1040 if you won t have the necessary documentation by the April 15 due date. Otherwise, you ll have to file an amended 2009 return to claim the credit an unnecessary pain.