I just remembered a conversation I had recently about why some investors obsess over certain numbers that most people ignore. It turns out there is a concept that many overlook when analyzing stocks: book value. It’s not the same as face value, even if it sounds similar. While face value is fixed at the time of issuance and only considers the share capital, book value is more alive, more current. It reflects the company's own resources at any point in its life, considering capital plus reserves. Some call it net asset value, and believe me, it’s essential if you practice value investing.

The difference between the market price and this book value is fascinating. The market not only values a company's intrinsic worth but is also influenced by feelings, expectations, sector trends. That’s why you see cases where a stock trades at 34 euros but its net asset value barely reaches 15. That’s where the P/NCV ratio comes into play, which simply divides the price by the net asset value per share. If it’s over 1, it’s expensive relative to book; if less than 1, it’s cheap. Let’s take an example: if a company has a net asset value of 26 euros per share but trades at 84, its P/NCV is 3.23. That screams overvaluation. Conversely, another with 31 euros of net asset value and a price of 27 gives 0.87, indicating relative undervaluation.

Now, how is it actually calculated? It’s quite straightforward: subtract liabilities from assets and divide by the number of shares outstanding. If a company has 3,200 million in assets, 620 million in liabilities, and 12 million shares, the net asset value per share would be approximately 215 euros. Publicly traded companies regularly publish these figures, so it’s not hard to find them.

But here’s the important part: this indicator has serious limitations. It doesn’t account for intangible assets, which is especially problematic in tech and software sectors where the real value lies in intellectual property, not machinery. That’s why you’ll see that tech companies almost always have high P/NCV ratios, but that doesn’t mean they’re overvalued; it just means the tool doesn’t work the same for all sectors. Also, book value depends heavily on how the accountant has presented the accounts. There’s what’s called creative accounting, where assets are inflated or liabilities minimized, and suddenly your numbers are completely distorted.

The case of Bankia is instructive here. In 2011, it went public with a 60% discount relative to its book value. It seemed like a bargain, but then came the disaster: disastrous results that led to its liquidation and absorption by CaixaBank in 2021. That shows that a low net asset value doesn’t guarantee anything about the future. Especially in small caps, young companies with scant books but huge future promises, this metric is almost useless.

In fundamental analysis, which is where this data really matters, net asset value is just one piece of the puzzle, not the complete solution. You need to look at macroeconomics, sector, management, earnings prospects. A stock cheap on book value is only a real opportunity if you’ve done the full research. So yes, knowing the net asset value gives you a perspective others ignore, but don’t make it your only criterion. It’s a backup, one more indicator among many.