• Big banks are sitting on $650 billion of unrealized losses, Moody's has estimated.
• It's a sign even Wall Street's best-known names are feeling the heat from the Treasury-market rout.
• Crashing bond prices sank Silicon Valley Bank earlier this year, and there may be more chaos to come.

Crashing bond prices sank Silicon Valley Bank in March — and there's reason to believe that what triggered the California lender's collapse may be haunting Wall Street again.

The brutal Treasury-market meltdown has hit some of the largest financial institutions hard, dragging down the share prices of big names such as Bank of America and fueling fears that the turmoil triggered by SVB's bankruptcy may not be over just yet.

Here's everything you need to know about unrealized losses, including why they're dragging on bank stocks and whether they could trigger another financial crisis.

Unrealized losses

Treasury bonds — debt instruments the government issues to fund its spending — have been on a nightmarish run since the onset of the pandemic, with investors fretting about rising interest rates and the long-term viability of the US's massive deficit.

BlackRock's iShares 20+ Year Treasury fund, which tracks longer-duration debt prices, has plunged 48% since April 2020. Meanwhile, 10-year Treasury yields, which move in the opposite direction to prices, recently spiked above 5% for the first time in 16 years.

As a result of that sell-off, some of the US's biggest banks are now sitting on unrealized, or "paper," losses worth hundreds of billions of dollars. That means the value of their bond holdings has plunged, but they've chosen to hold on rather than offload their investments.

Moody's estimated last month that US financial institutions had racked up $650 billion worth of paper losses on their portfolios by September 30 — up 15% from June 30. The ratings agency's data still doesn't account for a hellish October where the longer-term collapse in bond prices spiraled into one of the worst routs in market history.

These "losses" are not the same as debt, however, which describes actual borrowings that need to be repaid. 

Bank of America is the big lender worst affected by the crash in bond prices, having disclosed a potential $130 billion hole in its balance sheet last month.

The other "Big Four" banks — Citigroup, JPMorgan Chase, and Wells Fargo — have also racked up unrealized losses in the tens of billions, according to their second- and third-quarter earnings reports.

Another SVB-style crisis?

Silicon Valley Bank failed in March after disclosing a $1.8 billion loss on its own bond portfolio, triggering a run on deposits. Similarly, big banks' huge unrealized losses are also sparking concern among Wall Street doom-mongers.

"'Higher for longer' is absurd baloney," the market vet Larry McDonald said in a post on X Sunday, referring to the Fed signaling it would hold interest rates at about their current level well into 2024 in a bid to kill off inflation. "A 6% + Fed funds and Bank of America is near insolvency."

It's important to remember that BofA's $130 billion losses are still unrealized. Unlike SVB, it isn't officially in the red yet because it has not sold its bond holdings.

The bank's chief financial officer, Alastair Borthwick, shrugged off the market's worries on last month's earnings call, pointing out that most of the bank's fixed-income portfolio was low-risk government bonds it planned to hold until the debt expires.

"All of these are unrealized losses are on government-guaranteed securities," he told reporters. "Because we're holding them to maturity, we will anticipate that we'll have zero losses over time."

There's still a possibility that spooked BofA customers will pull their money en masse, as they did with SVB — but that hasn't happened. In fact, deposits are up after registering about 200,000 new accounts in the third quarter.

Some analysts also believe the worst of the Treasury-market rout is now over, with the Federal Reserve starting to signal that its tightening campaign is nearly done. Ten-year yields have softened in recent weeks, falling from 5% to 4.6% as of Tuesday.

Banks under pressure

That doesn't mean the Big Four banks can afford to just dismiss the bond rout.

In a paper published earlier this year, researchers for the Kansas City Fed concluded that paper losses could still drag down a bank's share price: "Unrealized losses can increase equity costs as investors' perceptions of financial health deteriorate."

That's been happening this year, with three of the big four banks' stocks sliding. Predictably, Bank of America has been worst affected, with its stock down 24% over the past year and 14% year-to-date.

"Worries over unrealized losses on sovereign bond holdings are also weighing on the US lenders, to again reflect concerns over rising interest rates and whether the US Federal Reserve will ultimately tighten policy by too much for too long," AJ Bell's Russ Mould said in a note last week.

Unrealized losses may not be about to trigger another financial crisis — but as long as bank stocks are down, they'll remain a concern for Wall Street's biggest names.