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Practicing golf in office
You can't put off finishing your taxes for much longer.
Jan Stromme—Getty Images

Remember the relief you felt last April when—faced with a looming tax-filing deadline—you simply applied for an automatic six-month extension for your 2013 return? The dread is back. October 15, next Wednesday, is the filing deadline for everyone who took advantage of the government’s grace period. As of the end of September, more than a quarter of the nearly 13 million taxpayers who had filed for an extension had yet to file, according to the IRS. If you’re one of those procrastinators, here’s what you need to know.

1. This time the deadline is real. No more extensions (one exception: members of the military serving in a combat zone). If you don't file and pay your tax bill, you'll get a failure-to-file notice. And you'll start the clock on a failure-to-file penalty (5% of your unpaid taxes per month, up to a max of 25%), a failure-to-pay penalty (0.5% of your tax bill per month, up to a max of 25%), and interest (currently 3%).

"You could have three things adding up month by month if you do nothing by October 15," says Mark Luscombe, principal federal tax analyst for Wolters Kluwer, CCH. Of course, if you're expecting a refund, there's no penalty for not filing—and also no refund until you do.

2. Do nothing, and the IRS will eventually file for you. And you may not like the results. That's because the IRS will base your tax bill on the information it has, such as the income reported on your W-2, notes White Plains, N.Y., CPA Paul Herman. But they won't know other things that could lower your tax bill, like all the deductions you're entitled to or what you paid for stocks, bonds, or mutual funds you sold last year.

3. If you can’t pay your entire bill, throw out a number. File your return for sure—that at least saves you the failure-to-file penalty. When you do, request an installment agreement (Form 9465), and propose how much you can pay a month, or the IRS will divide your balance by 72 months. If the offer is reasonable, says Herman, the IRS may accept it.

4. Free help hasn't gone away. Through October 15, you can still use the IRS's Free File program, which makes brand-name tax-filing software available at no cost if your income is $58,000 or less. Earn more than that, and you can still use the free fillable forms at the IRS website.

5. You have one less way to cut your taxes. You’re out of luck if you had hoped to trim your tax bill by funding an individual retirement account for 2013 (depending on your income, as much as $5,500 was deductible last year, $6,500 if you're 50 or older). Even though you got an extension to file, the deadline for opening an IRA for 2013 was last April 15. (Make a note: You have six months to open a 2014 IRA).

However, if you switched a traditional IRA into a Roth IRA last year—which meant a tax bill on your conversion—you still have until October 15 to change your mind. That's something you might do if the value of your Roth has since dropped. You can "recharacterize" the conversion (in effect, switch back to a regular IRA) and then convert to a Roth again later, this time realizing a smaller taxable gain and owing less in taxes.

Finally, if you find yourself doing your taxes every fall, think about changing your ways. Maybe invest in a better system for organizing your records? "If you waited this long," says Herman, "try to begin planning earlier for next year."