Vanguard Group looks set to add more than $200 billion in new assets during 2015 for a second straight year, taking the total to $3.5 trillion.

It could be a bit more. But the Malvern mutual-fund giant is minimizing the value of one asset in every Vanguard fund's portfolio: shares of Vanguard Group Inc., the company that manages Vanguard's funds. Every Vanguard fund (and, through the funds, every Vanguard shareholder) owns a piece of Vanguard Group.

How much is Vanguard worth?

Vanguard is a private company, so you can't buy Vanguard Group shares on the stock market. Still, Securities and Exchange Commission rules oblige mutual funds to list the values of even the private-company stocks they own, as Vanguard does, for example, with shares of Uber, the ride-share company.

Private shares like Uber's "are valued by our pricing review committee" using "market valuations of publicly traded peers," as well as private transaction prices, Vanguard spokesman John Woerth told me.

So let's compare Vanguard and its publicly traded peers. Rival BlackRock, with $5 trillion in client assets (a third larger than Vanguard) and $15 billion in yearly revenues (triple Vanguard's yearly fees), has a stock market value of $58 billion. Federated Investments (with $350 billion in assets and $900 million in revenues, both a fraction of Vanguard's) is worth $3.5 billion.

Maybe Vanguard's value would fit between those two, in the low tens of billions.

But, including all its funds, Vanguard reports its valuation to investors and the Securities and Exchange Commission at just $250 million, a small fraction of what its size and cash flow would seem to indicate.

That value represents the "capital contributed" to Vanguard by the funds in the past, Woerth told me, not current market value.

Isn't that like giving investors an initial public offering stock price instead of today's quote?

"Vanguard's a private company, so we do not think about a 'mark to market' valuation, because there is no market for our shares," Woerth told me. Uber, of course, is private, too, but Vanguard's funds give it a market value.

Woerth's point is that Vanguard has no intention of being sold. However, the fund-service agreement between Vanguard and its mutual funds does provide a directive to value its assets if the company is ever dissolved, for example, in a sale. We have seen formerly customer-owned banks (PSFS) and insurers (Provident Mutual) converted to stock corporations in the past, sometimes very profitably.

The Vanguard funds' recent filings with the SEC are due to "an SEC audit" that Woerth says is "unrelated to tax issues." The company is providing new details on financial relationships between the funds and Vanguard Group.

In addition to financial and professional services expenses (Vanguard has long reported its management-fee ratios), Vanguard funds have begun noting in their liability statements that they also owe "Payables to Vanguard."

The "Payables," a footnote says, include operating costs "such as deferred compensation/benefits and risk/insurance costs." For all Vanguard funds, these "Payables" total more than $3 billion.

The filings note that the funds don't have to pay Vanguard this money during the current reporting period. Which is probably good: At several times the company's capital investment valuation, $3 billion sounds like a lot, even for a company as successful as Vanguard.