WASHINGTON — The devil may wear Prada, but the tax collector doesn't seem to care.

Mere mortals don't get a pass, either. The U.S. Tax Court in Washington recently ruled against a New York investment banker who claimed nearly $49,000 in deductions for charitable property contributions consisting almost entirely of designer clothing. In a written opinion, Special Trial Judge Lewis Carluzzo said her only sin was to be "overly optimistic" about the worth of the clothes, which commanded high prices when sold new.

"Deductions are a matter of legislative grace, and taxpayers who claim deductions must establish entitlement to them," he wrote.

Such are the pitfalls awaiting fashionistas as April 15 nears. Many are constantly reinventing themselves with a new Hermes Birkin bag or pair of red-soled Christian Louboutins. They bring out a different Versace gown to each charity ball; their favorite date for cocktail parties is Marc Jacobs. And when they're done, the frocks are destined for the donation bin or consignment shop.

But come tax time, when they take stock of how much such worldly possessions are worth, they are often disappointed.

"When you work with consignors, that is the biggest issue," said Liberty Jones, who runs Alex Boutique in Washington. " 'Well, I wore this to the Corcoran Gala.' Well, it doesn't matter. ... They add a little bit of emotion to it and they think it's more valuable than it is."

According to the court decision, investment banker Christiana Stamoulis of Goldman Sachs describes herself as an "impulsive buyer" who frequently wore items only once or twice before donating them to Housing Works Thrift Shops in New York, a nonprofit that serves people with AIDS. In 2002, when she claimed her deductions, she charged $53,916 in clothing and $9,253 in shoes to her credit cards. Her adjusted gross income was just under $115,000. She claimed $48,954 in non-cash deductions for property.

Stamoulis also claimed $5,917 in cash contributions and an $893 carryover from the previous year, bringing her total charitable tax deductions to $55,764 in 2002.

Her donations went mostly to Housing Works. Her attorney, Ronny Buni, said Stamoulis donated more than 100 items to the thrift store that year, which the court did not dispute.

In his opinion, Carluzzo acknowledged that determining the resale value of couture clothing was "at best, an inexact science." At Alex Boutique, Jones said, a top consignor can donate more than 200 items a year, with a total resale value of about $85,000 — less than two-thirds of the original cost of the clothes.

Inga Guen, owner of the high-end Washington consignment shop Inga's Once Is Not Enough, said items typically resell for about 20 percent of the original price. The shop keeps 10 percent, and the remainder goes to the consignor. Items that do not sell may be donated to charities, which then qualifies the original owner for a tax deduction.

"You must understand everything depreciates," Guen said. "Housing, cars and mostly clothing." For example, the beaded pink Chanel gown currently in stock, which originally cost about $7,000, is selling for $1,200, she said.

It is the donor's responsibility to determine the clothing's fair-market value for tax deductions. Stamoulis estimated hers in part by tracking auctions on eBay, Buni said. But she never printed evidence of the auctions or followed them to the end. Nor did she check on the price Housing Works charged for her clothes or similar items.

In the opinion released last week, the judge found that Stamoulis' charitable property contributions were worth only $8,949. The IRS requested $14,649 in back income taxes and $2,930 for an accuracy-related penalty; Stamoulis has disputed the amounts.