The deadline for filing taxes is 26 days away, a countdown that's costing many veteran and novice taxpayers a good night's sleep.

"I know the deadline, but I don't know what I'm required to submit," said Jennifer Ash, 22, who graduated from George Mason University in May and will pay taxes for the first time on a full-time job. "All the forms are in different places. I'm afraid of leaving something out. I don't want the IRS coming back years later saying I owe them thousands of dollars."

Ash at least has collected her paperwork in one place — W-2 forms stating her wages for the year, college-loan payment stubs and totals paid in interest, receipts for charitable giving and for the Treo smartphone she uses mostly for work. Being organized is more essential than ever: The Internal Revenue Service has cracked down on receipts, requiring one for even tiny claims.

"If I had to give one piece of advice to anyone, keep receipts and keep them for three good years past when you file your return," said Stef Tucker, an attorney with Venable.

But being organized won't necessarily make the rules easier to fathom — if you can find out about them in the first place. Many taxpayers simply won't take advantage of breaks, experts say.

As of mid-February, 10 million taxpayers, or about 30 percent of those who had filed, did not request a one-time refund of a telephone excise tax that ranges from $30 to $60 and that nearly everyone can claim.

And while most folks know the peril of filing late if they owe the government money — penalties, interest charges, scary letters and potential visits from IRS agents — many may not know that filing too early can also have drawbacks. The 1099 form summarizing dividends and interest payments that banks, brokerages and other financial firms send clients in January often is revised in February or March, requiring taxpayers to amend returns.

Not until Feb. 3 could IRS computers handle 2006 returns claiming breaks Congress extended at the last minute last year, including deductions for state and local sales taxes, higher-education tuition and fees, and teacher expenses. Electronic forms filed before Feb. 3 that claimed any of these breaks must be resubmitted, while paper versions were set aside to process after that date.

As always, taxpayers need to remember the distinction between tax deductions or exemptions, which reduce the amount of income that is taxable, and tax credits, which reduce the actual amount of tax owed.

Low-income wage earners who claim the earned-income credit may also qualify for the saver's credit, which Congress recently made permanent. It permits a family earning $50,000 or less that puts money in a work retirement plan to cut a tax bill or boost a refund by up to $1,000.

Wealthier taxpayers must calculate taxes first under regular rules, then under the alternative minimum tax (AMT), and pay whichever is higher. The AMT was created in 1969 to target 155 wealthy tax-dodgers, but because it's not indexed for inflation, it could affect an estimated 4.2 million families when they calculate their taxes next month. Taxpayers in high-tax jurisdictions are especially vulnerable. (Unless Congress changes the law, 19 million more households, many earning as little as $50,000 a year, could end up paying the tax next year, as would nearly half of all taxpayers by 2017.)

All taxpayers should take advantage of retirement credits — you have until the April filing deadline, for example, to invest in an individual retirement account for 2006.

A recent survey of nearly 1,300 adults by CCH, a tax-consulting firm, found that 18-to-24-year-olds are the least likely to participate in tax-advantaged retirement plans, such as 401(k)s. A new law lets companies automatically enroll new workers in such plans, but the survey found that young adults say their employers don't explain these programs well or help workers take full advantage of them.

New graduates need to know the rules governing work-related tax deductions. First, itemizations must exceed the standard deduction, which this year is $5,150 for a single adult, said David Sharkey, a certified public accountant with Ryan, Sharkey & Crutchfield in Herndon, Va.

Mortgage interest, taxes on a home or car or boat, charitable contributions and unreimbursed employee expenses are all potential claims to itemize.

Taxpayers with adjusted gross income of $52,000 or less — attention recent college graduates — can have their taxes prepared free through the IRS "Free File" program on the agency's Web site, www.irs.gov.