You've put off filing for 105 days, but any more procrastination could cost you. So don't just sit there.

Actually, do sit there just a bit longer. Stick with Bankrate.com, and we'll walk you through what you have to do today to get the Internal Revenue Service what it wants.

Don't ignore the IRS
The key to surviving last-minute tax filing is realizing that the IRS will not be ignored.

These guys aren't kidding around when they set deadlines. The IRS wants your paperwork, and it wants it now. If you don't file your return today and you owe taxes, you may owe an additional penalty for failure to file unless you can show reasonable cause. The assessment is 5 percent per month (or any part of a month, even just a day) of your balance due.

Tax penalties

• Not filing your return will cost you an additional 5 percent each month of any due tax. • Not paying what you owe will add an extra charge of 0.5 percent each month of your due tax amount to your overall IRS debt. • If you haven't filed or paid, the combined penalty rate is 22.5 percent. • If you don't file or pay for five months, the 0.5 percent failure-to-pay penalty will accrue, up to 25 percent of what you owe, until the tax is paid. • In that case, the total penalty for failure to file and pay could amount to a 47.5 percent of your tax bill. • Interest also is charged on the overdue amount.

Even if you file on time but don't pay what you owe, the IRS can charge you. This nonpayment penalty is one-half of 1 percent of the tax due each month, or any part of a month, that isn't paid. The fine continues until it reaches 25 percent of your late payment.

If both penalties apply in any month, you get a small break on the failure-to-file penalty. The IRS will reduce it by what it's charging you for not paying, making your potential maximum nonfiling penalty "only" 22.5 percent.

But when you combine the late-filing and nonpayment penalties, even with the IRS "discount" on the late-filing charge, your total tax penalties could be substantial if you continue to ignore your tax responsibilities. Put off filing and paying for five months, and the 0.5 percent failure-to-pay penalty continues to run, up to 25 percent, until the tax is paid. This means your total penalty for failure to file and pay could amount to a whopping 47.5 percent (22.5 percent for late filing, 25 percent for late payment) of the tax owed.

The IRS also charges interest, currently 6 percent, on the amount of tax due. The rates are adjusted quarterly.

And if your return is more than 60 days late, the minimum failure-to-file penalty is the smaller of $100 or 100 percent of the tax required to be shown on the return.

Interest charges also will continue to add up -- on the penalties, too. So let's get started and get your taxes done!

Another shot at postponement
Since you've waited this long, you might be inclined to put off the inevitable a bit longer. Guess what? You can -- sort of.

The IRS will wait for your return until Oct. 15 if you file for an automatic extension. You can do this by sending in Form 4868, Application for Automatic Extension of Time to File. You can e-file the extension request from your home computer or have your tax professional who is an IRS authorized e-filer do so for you. Regardless of which method you choose, the extension request also must be made by April 15, or postmarked with that date if you snail mail it.

The extension will give you six more months to get your tax act together. But you don't have to wait until that ultimate deadline. Any time you get your tax filing material in order before then, you can send in your 1040.

Pay anyway
Filing this form won't delay any money you owe Uncle Sam. While he'll wait patiently for your paperwork if you ask, he wants the money on its way today or all those interest and late-payment fees will be tacked on to your final bill.

How do you know how much to send? You don't have to be precise. As long as the amount comes to 90 percent of what you eventually owe when you crunch all the numbers, you'll be OK with the IRS.

The easiest way to estimate the amount to pay is to look over last year's tax return. If your financial and tax situation are basically the same as last year -- you have the same job, still married, two kids, deductible mortgage interest -- then what you owe this year is likely to be close to the amount you owed last year.

Choosing your form
By now, you may have decided that it's just as easy to file and be done with it. In that case, your first step is to pick which form to use. The IRS gives you three options: the 1040EZ, the 1040A and the long 1040.