The new year is here, but if you pay estimated taxes you have one more filing task before you can close out last year. Your final estimated tax voucher of 2008 is due Jan. 15.

Estimated tax filings usually are due the 15th of each January, April, June and September, except when that date falls on a weekend or holiday. This latest payment is the fourth and final one for the 2008 tax year. It accounts for money you earned, but didn't have income tax withheld from, in September, October, November and December.

However, you might be able to avoid this payment entirely. If you file your regular 2008 return and pay any taxes due by Feb. 2 instead of the April deadline, you can skip this last 1040-ES filing. (The usual date for filing to avoid the mid-January filing is Jan. 31, but since that falls on a Saturday in 2009, the next business day, Feb. 2, becomes the IRS-approved due date.)

Estimated tax payments are the bane of an increasing number of Americans. They are expected from people who make money on investments, operate their own businesses or get any extra cash that has not yet been taxed.

Time-consuming? Yes, nobody really likes doing taxes more than once a year.

Confusing? Sometimes, especially if you're earning income from several different sources at different times.

Necessary? You bet, or you could end up owing Uncle Sam penalties and interest.

The reason behind estimated taxes
Most people meet their tax obligations through paycheck withholding.

If you're self-employed, either as your main job or as a sideline, you must get the taxes on this money to the IRS yourself by filing Form 1040-ES. Estimated taxes also are due on interest and dividends, profits from investment sales, alimony, rental income and prizes or awards.

The estimated tax system was designed to ensure that taxpayers who have a lot of nonwithholding income pay into the tax system regularly. This evens things out between these taxpayers and wage earners who lose a chunk of money each paycheck to taxes.

The problem, says Linda Durand, a CPA with Drolet & Associates PLLC in Washington, D.C., is too many folks who have a windfall get excited about the extra cash and immediately spend the proceeds without any thought to the tax implications. Even people who earn a steady stream of money that isn't taxed upfront put off filing estimated taxes because they want or need the cash now. They figure they'll make it right with Uncle Sam come April 15.

That's not a good idea. If you end up owing $1,000 or more in April, you might have underpaid your tax bill. That would open the door for the IRS to add penalties and interest for not paying tax on your earnings as you got them.