AGNC Investment (AGNC 0.94%) has a gigantic 15%+ dividend yield. That lofty yield sounds very enticing, but sometimes things that sound too good to be true are, in fact, too good to be true. Here's why investors need to take a very nuanced view of AGNC Investment and how the company may actually be helping you decide when to buy the stock.

What does AGNC Investment do?

Property-owning real estate investment trusts (REITs) buy physical properties and lease them out to tenants. That's what you would do if you owned a rental property, so it's probably fairly easy to wrap your head around the business model. Mortgage REITs like AGNC Investment buy mortgages that have been pooled together into bond-like securities. That's a lot more complex and you probably couldn't mimic that in your own investment life.

A person looking at a computer screen with a look of unpleasant surprise.

Image source: Getty Images.

Everything from interest rates to mortgage repayment rates can impact the value of mortgage securities. So even tracking what is going on within AGNC Investment's portfolio, or within any mortgage REIT, would be hard for most investors. Adding to the complexity is that mortgage securities trade all day long, so the portfolio's characteristics can change fairly quickly.

This is not an investment for conservative income investors. That fact is highlighted by the steady downtrend in the dividend over the last decade or so, as the chart below highlights. Not surprisingly, the price of the stock has trailed the falling dividend.

AGNC Chart

AGNC data by YCharts

What is AGNC Investment worth?

That said, AGNC Investment's value is basically the value of its portfolio of mortgage securities. In that way it is kind of similar to a mutual fund. And, like a mutual fund, AGNC Investment reports the value of its portfolio on a per-share basis. It calls this number tangible net book value per share. It only reports that number quarterly, but it is an important figure to monitor.

At the end of the first quarter of 2025 AGNC Investment's tangible net book value per share was $8.25. At the end of the first quarter of 2022 it was $13.12. Tangible net book value per share can rise and fall fairly dramatically at times, depending on the market environment. Over the past year, for example, this metric has risen and fallen by 5% between quarters multiple times. It is, at best, a rough gauge for investors to monitor between quarters.

But the really interesting thing here is that AGNC Investment's stock price often trades above tangible net book value per share. Sometimes dramatically above the number -- the 52-week high is $10.85 even though the reported tangible net book value per share never rose above $8.84 in any of the last four quarters.

This is great news for shareholders, since AGNC Investment frequently sells new shares to the public to raise additional capital. Every penny above tangible net book value that a new buyer pays is tantamount to giving current shareholders free money. Management even explains this fact when it discusses stock sales, saying things like the company "opportunistically" raised money "at a considerable premium to tangible net book value" and that this brings "meaningful book value accretion to our common stockholders."

AGNC Chart

AGNC data by YCharts

The takeaway here is pretty clear. Nobody should pay more than tangible net book value per share for AGNC Investment unless they believe that number is going to be headed sharply higher. But sometimes AGNC Investment's share price dips below that figure, with the 52-week low coming in at $7.85. The company would likely not be raising capital at that price, given that it would destroy value for current shareholders. However, if you buy the stock on the open market below book value you are increasing the chances that you are getting a good deal on the stock.

AGNC Chart

AGNC data by YCharts

The fly in the ointment is the dividend

The problem with this discussion is that it doesn't address the dividend or the dividend yield. That's because the company's focus isn't income, it is total return. The dividend is a part of total return, but total return assumes the dividend is reinvested. But a key part of total return is also the price you pay for the investment.

If you bought at the 52-week high price of $10.85 per share, your total return would be terrible here even with the huge dividend yield. However, if you kept a close eye on tangible book value per share and only bought when the stock price was at or below the last reported figure, your total return would likely still be positive, helped along by that lofty yield.