ATLANTA -- Monday is not only the deadline for filing 2010 taxes, it's also an important day for Americans who are owed a collective $1 billion in unclaimed funds.
Nearly 37,000 Metro Atlantans are among the taxpayers who either didn't file taxes or didn't claim all the money they were due from 2007. Monday is the deadline for claiming that money. The median refund is nearly $600.
Post offices around the region will stay late to accept tax forms.
* 1960 Lexington Road, 30605 -- closes at 7 p.m.
* 1695 South Lumpkin Street, 30606 -- closes at 7 p.m.
* 400 Pryor Street SW, 30303 -- closes at 8 p.m.
* 3900 Crown Road SW, 30304 -- closes at 11:59 p.m.
* 575 Pharr Road NE, 30355 -- closes at 8 p.m
* 1410 Atlanta Highway, 30040 -- closes at 8 p.m.
* 520 West Ponce de Leon Avenue, 30030 -- closes at 6:30 p.m.
* 1557 Buford Drive, 30043 -- closes at 7 p.m.
* 4455 Lower Roswell Road, 30068 -- closes at 7 p.m.
* 428 Crosstown Drive, 30269 -- closes at 7 p.m.
* 4644 Powder Springs Dallas Road, 30127 -- closes at 6:30 p.m.
* 10719 Alpharetta Highway, 30076 -- closes at 7 p.m.
* 227 Sandy Springs Place NE, 30328 -- closes at 8 p.m
With the deadline just hours away, filing for an extension may provide a way to avoid last-minute mistakes that could cost you money.
To request an extension until Oct. 17, file IRS Form 4868. Approval is automatic, but you must file the form by midight to avoid late-filing penalties.
RELATED: Free tax help
You can fill out the form and mail it before midnight or submit it electronically. Some tax software providers will e-file your extension for free. If your 2010 adjusted gross income was $58,000 or less, you can use the Free File program, a partnership between the IRS and tax software companies, to e-file the form. For more information, go to freefile.irs.gov.
H&R Block's 7,000 company-owned offices and most of its 4,000 franchises will help taxpayers file extension forms for free.
Taxpayers aren't required to hire H&R Block to prepare their taxes to take advantage of the promotion, spokeswoman Kate O'Neill Rauber said.
An extension will give you more time to file your return, but it won't give you more time to pay. If you owe the IRS money and don't pay by Monday, you'll owe interest and penalties on the unpaid balance.
To avoid that unhappy outcome, estimate how much you owe and include that amount when you file your extension. Don't lowball: The IRS may deny your extension if you underpay by too much, said Bob Meighan, vice president of TurboTax.
Between 20 percent and 25 percent of taxpayers file their returns during the last two weeks of the filing season, according to the IRS. TurboTax has seen a slight increase in last-minute filings, which may reflect the growth of online tax programs and e-filing, Meagan says.
"People can wait, not only until the 11th hour, but the 12th hour," to file, he said.
Most taxpayers receive a refund, and this year the average refund is nearly $3,000. That's a powerful incentive to get down to business and file your return. If you're rushing to beat the deadline, here are some errors to avoid:
* Forgetting to claim the Making Work Pay credit. The 2009 economic recovery act included a credit of up to $400, or $800 for married couples who file jointly. Most workers received the credit in their paychecks through lower withholding. But even if you received the money, you still have to claim the credit on Schedule M of your tax return.
Tax software will do this automatically, but paper filers need to manually fill out the form, Meighan said. Otherwise, you could end up paying an additional $400 to $800 in taxes.
* Math errors. Math miscalculations are among the most common errors found on tax returns, according to the IRS. If you're not comfortable using an online or desktop software program, at least consider using the IRS Free File Fillable program, which provides electronic versions of paper forms. You won't get the kind of advice you get from tax software, but the program will do the math for you. Once you're done, you can file electronically or print the forms and mail them.
You can find the program at www.freefilefillableforms.com.
* Overlooked tax documents. Tax software gets better all the time, but there are some problems it can't diagnose, Meighan said. If you leave out a W-2 or 1099, your tax software program can't comb through your files and find them for you. If you've misplaced some documents or think some haven't arrived yet - and depending on the type of investments you have, that may well be the case - file for an extension.
* Insufficient postage. Beating the filing deadline won't do you any good if your return comes back postage due. And, in what seems like spectacularly bad timing, postage rates increased on Sunday. The rate for a first-class stamp remains 44 cents, but the cost of each additional ounce rose from 17 to 20 cents.
So it might not be a bad idea to weigh your return before you drop it in the mail slot.
(USA Today contributed to this report.)