Tax season is famous for its procrastinators. In some places, visiting the post office late on April 15 (or April 17, which is this year's deadline) is almost like a town party, with dozens of people taking advantage of late hours to get that precious last-day postmark on their returns. But on the other end of the spectrum are the people who are in a rush to get everything done. These are the people who ask their employers to get them their W-2 salary forms early and have estimates of all their income and expenses over the entire year. They could give you a draft of their tax return by the first week of January. Once those 1099 forms from their investments come in the mail, these folks are ready to go.

Unfortunately, it often doesn't pay to jump the gun trying to get your taxes done early. Even though most employers and financial services companies are required to get tax forms to you by the end of January, it's all too common that those forms have errors on them that are only discovered after they're sent to you. If you start doing your taxes based on these erroneous forms, you may find yourself having to start over or even needing to file an amended return if you get a corrected form in the following weeks or months.

Tax-code complications
With all the complex provisions in the tax laws, it's almost unfair to expect brokerage firms and other companies to get all the information they need in order to send you an accurate 1099 tax form. For instance, consider the typical brokerage account. Dealing with individual stocks and bonds is relatively easy; the dividends and interest payments have been collected throughout the year, and tallying them is a straightforward exercise. Once you start dealing with mutual funds, however, you have a whole new set of challenges. To give you accurate information about special tax treatment for items like capital-gains distributions, qualified dividends, and tax-exempt interest, brokerage firms have to get more information about your mutual fund income from the fund companies. But in general, mutual fund companies must follow the same rules as everyone else; they must therefore send out information about taxable income to shareholders by the end of January. Yet if brokerage firms that hold mutual fund shares for their clients' accounts don't even receive the information about the fund distributions until the day they're supposed to send it out to you, something has to give.

This year, at least a few firms, including Wachovia (NYSE:WB) and Morgan Stanley (NYSE:MS), have asked for extensions on the Jan. 31 deadline. The common solution that brokerage firms use is to send out a 1099 based on whatever information the firm has already received in order to comply with the Jan. 31 deadline. If the firm gets additional information that requires a correction, then it will send out corrected 1099s later on. Usually, firms send out these corrected 1099s in advance of the April deadlines, but they are dependent on receiving the necessary information from outside sources and so must wait until it is made available to them.

When corrections aren't right either
Even if you get corrected tax forms from a financial institution, you can't necessarily rely on their numbers. Especially when it comes to things like qualified dividend treatment, the tax laws are too complicated for financial firms to report your income accurately. One problem is that in some cases, the tax treatment of certain income depends on actions you take after the end of the tax year. For instance, in order for a dividend on a stock to qualify for favorable tax treatment, you have to own the stock for a certain period of time; the technical rule is that you must own it for at 61 days over the four-month period surrounding the date of the dividend. So if you bought a stock on Dec. 28 and it paid a dividend on Dec. 29, you won't yet know if you can treat the dividend as qualified. If you sell the stock on Jan. 31, then the dividend won't count as a qualified dividend. If you wait to sell it until March 1, on the other hand, it will be qualified. Since your brokerage firm has to send out a 1099 form well before it can be sure about your qualified dividends, it will have to make assumptions about your income.

If you discover an error on your W-2 or 1099 forms, the best solution is to ask whoever issued the tax form to make the necessary corrections and then have them file a corrected form with the IRS. If you simply make the corrections on your own tax return, then the information on your return won't match the computerized records that the IRS holds based on the reports it gets from your employer and the financial institutions where you have accounts. A discrepancy between the totals on your return and the figures reported by your employer and financial institutions will often result in an IRS inquiry and may lead to a full-blown audit. Although you may well have the documentation necessary to prove that your numbers are the correct ones, you can save yourself a lot of hassle by getting a corrected form filed.

The key to beating procrastination is just to decide to get things done early. Occasionally, though, trying to do things too early ends up making more work for you. When it comes to tax forms and doing your taxes, it pays not to jump the gun.

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Fool contributor Dan Caplinger won't file his taxes until mid-April this year, but he'll have everything ready to go well before then. He doesn't own shares of any of the companies mentioned in this article. The Fool's disclosure policy is never late.