NEW YORK — Checking to see which bank is revealing billion-dollar losses in its portfolio has become something of a daily routine on Wall Street. Yesterday, traders fretted about Barclays' multibillion-dollar write-down over their morning coffee.

The British bank estimated it would write down $2.7 billion for losses on securities linked to mortgages for borrowers with poor credit. Barclays, along with Wells Fargo & Co., SunTrust Banks Inc. and General Electric Asset Management, joined the slew of financial companies anticipating, in total, more than $30 billion in losses this quarter.

That figure doesn't exceed the approximately $44 billion written down by financial institutions in the third quarter, but the fourth quarter is only halfway over — leaving investors wondering how many more write-downs are on the way.

"We have not seen a nationwide decline in housing like this since the Great Depression," said Wells Fargo CEO John Stumpf.

Many investors are bracing for UBS AG to report a substantial write-down — a Lehman Brothers analyst is reportedly estimating a write-down of $7 billion to $8 billion. However, the Swiss bank said it expects to post a fourth-quarter profit.

A write-down is a calculation of how much one's debt holdings — in either actual mortgages, or instruments like CDOs that have mortgage exposure — have lost value.

Because it's so hard to know how much some investments are worth in the tight credit markets, Wall Street remains uncertain how high losses really are. Certain accounting rules require companies to price their holdings according to the market value; when there is no market, they have to estimate.

Neri Bukspan, chief accountant for Standard & Poor's credit market services, likened the process to figuring out how much your house is worth when no one in your neighborhood can sell theirs — a scenario many U.S. homeowners can relate to right now.

"Some argue this is highly judgmental, that management could introduce their own bias," Bukspan said.

Furthermore, if the credit markets worsen, banks will inevitably have to write down their portfolios further.

The credit markets tightened up in August when concerns about plummeting home prices and missed mortgage payments came to a head.

Industry experts say home prices will likely keep falling because lending standards were the most lax in late 2006 and early 2007. The adjustable-rate mortgages issued then won't reset until late 2008 or early 2009, so investors should brace for a couple more years of increasing foreclosures — and in turn, scarce demand for mortgage-backed securities.