Filing on deadline? You're not alone.

Tax preparer Eva Rosenberg figured she had heard every excuse for missing the April 15 filing deadline. Then, about a decade ago, one client reeled off a wild litany.

First, high water flooded the woman's home in Malibu, Calif. Then she moved inland, where a wildfire in the Santa Monica Hills destroyed her apartment. She moved again. An earthquake hit.

"Everything that could happen to that woman happened," recalls Ms. Rosenberg, who says her client had evidence to support her story and eventually sent the data needed to file.

It's that time of year again, when everything from incomprehensible instructions to lost receipts conspires to prevent Americans from filing their federal tax returns on time. Typically, about one-quarter of taxpayers file in the last two weeks, sometimes applying NASCAR driving techniques to reach a post office before the April 15 midnight deadline. A growing number don't make it and have to file an extension.

Why so many Americans are lax - and getting more lax - about filing taxes remains something of a mystery. Among the suspected factors: more complex forms and taxpayers with busier lives.

"The average person doesn't live and breathe taxes," says Denise Sposato, a spokeswoman for H&R Block in Kansas City, Mo. They know about changes, she says, but may be unprepared to encounter them.

Then there's old-fashioned procrastination. When Ipsos Public Affairs polled Americans between April 4 and 6 this year, 14 percent had not even begun preparing their taxes.

In what the Internal Revenue Service calls a major milestone, a majority of federal returns by individual taxpayers will arrive electronically this year. But observers doubt that heralds the end of an almost carnival-like rite of spring.

Last year in Santa Barbara, Calif., post office workers dragged mailboxes to the curb and turned them to face the street to facilitate late-night drive-bys.

"It was more jovial than anything," says Peter Sklar, who runs edhat.com, an online city guide. Drivers, some in pajamas, seemed to take pride in their late-game heroics, he says.

"They were laughing at themselves," says Mr. Sklar, who recalls a restaurateur walking down the line of cars, handing out coupons. "People were saying they'd just started [the paperwork] at four that afternoon."

What about his own state of affairs this year? Speaking from his cellphone atop a mountain at Heavenly Valley ski resort on the California-Nevada border, Sklar admits he has yet to begin. The data usually go to his accountant about now, he says, "and she files for an extension."

That's an increasingly popular option. About 3.5 percent of federal-tax filers used an extension in 1983, according to the IRS. In 2003 the figure passed 6.5 percent. In more than 8 million cases last year, an extension kept the IRS at bay.

Late filers don't ruffle Uncle Sam, though IRS officials note that extensions are meant to allow people more time for filing forms, not sending payments. Even if paperwork trails behind, filers should send an estimated payment by April 15, they urge.

Some citizens take lateness to its extreme. Nonfilers account for about $30 billion a year of lost federal revenue, says Nancy Mathis, an IRS spokeswoman.

Not all nonfilers owe money. The IRS announced last month it had $2 billion in unclaimed refunds awaiting about 1.7 million nonfilers from 2001. After Friday, those funds can't be retrieved.

One recent study attempted to profile nonfilers as a group by looking into the cases of some 3,000 Arkansas residents who had filed federal taxes but sent no forms to the state.

"There's really a lot of unintentional noncompliance," says Christina Ritsema, professor of accounting at Hope College in Holland, Mich., and one of the study's three authors.

About half of the 900 people who responded to the team's queries said they had lost track of the duty. Some were distracted by a divorce. Others had forgotten. Still others lacked the knowledge to complete the forms - or the money to have them prepared.

Of the half that had intended not to file, Professor Ritsema says, 52 percent were owed money, but either did not know that fact or did not want to bother with the process of getting the refund.

Generally, lower-income and single people expressed the strongest desire to become compliant, says Ritsema. Higher-income individuals "needed some external motivator." About 7 percent of respondents wanted to come clean but worried about the consequences of coming forward.

Attitude can affect the way late-filing cases play out.

Several years ago, a New York attorney postponed tax filing so that he could finish some casework before a pending suspension began, according to A.J. Cook, a lawyer and accountant with the Memphis, Tenn., law firm Pietrangelo Cook. Taken to court by the IRS, the lawyer was fined and told his priorities were misplaced, writes Mr. Cook in an e-mail.

About the same time, two brothers who ran what Cook calls "a maze of businesses" signed an accountant-prepared return and got it into the hands of their company treasurer in March. He misplaced it.

It didn't resurface until mid-May, when the treasurer rushed it to his secretary to send by registered mail. The secretary stamped it using a postage meter and left it for pickup. On June 27, a janitor found the return behind the meter, and mailed it.

When the IRS assessed a late penalty, the brothers went to court. In what Cook calls "a fair but surprising decision," the judge ruled that they owed no penalty. They had relied on people and procedures previously successful in filing returns, said the court. Employees had corrected the problems as soon as they had discovered them.

Rosenberg, who also runs TaxMama.com, has this general advice on filing taxes: Just do it.

She has met as many types of filers as she has heard excuses. One of them, she says, feels an annual need to rebel against giving the government money.

"He refuses to have withholding taken out of his paycheck, and then always pays a humongous tax, with penalties and interest," she says.

Another, a perfectionist, just dallies over loose ends.

Once, "all I needed from her was her mortgage information and charitable contributions. I had everything else ready to go in February. [But] she did not file until the following year's August," says Rosenberg. "And she had refunds coming."