I just noticed that many investors confuse two concepts that seem similar but are actually very different: the nominal value and the net book value of a share. Today I want to delve into the latter because it is fundamental if you want to do serious fundamental analysis.

When we talk about net book value, we are basically referring to what portion of the company's real resources belongs to each share. It is not what it cost to create the share when it went public, but what it is actually worth according to the accounting books right now. That is, you take all the company's assets, subtract the debts, and divide by the number of shares. That is the formula for net book value in its simplest form.

That’s why it’s also called Book Value in English. And this is where Value Investing comes into play, the style of investing that seeks to find companies trading below what they are truly worth according to their balance sheets. The idea is to buy cheap and wait for the market to realize the mistake.

Now, the formula for net book value is straightforward: (Assets - Liabilities) divided by the number of shares outstanding. But here’s where it gets interesting. Imagine a company with assets of 3.2 billion, debts of 620 million, and 12 million shares. Doing the math: 2.58 billion divided by 12 million gives you 215 euros per share. That is your net book value.

What many don’t understand is that this number rarely matches the price the share has in the market. The market also considers expectations, sentiment, sector trends. That’s why the P/B ratio exists, which is simply the price divided by the net book value. If it’s 1, it’s in line. If it’s greater than 1, it’s expensive. If it’s less than 1, it’s theoretically cheap.

Let’s take two Spanish companies that often appear in these analyses. One trades at 84 euros with a net book value of 26 euros, giving a ratio of 3.23. That means you are paying more than triple what it’s worth on the books. Another company trades at 27 euros with a net book value of 31 euros, ratio of 0.87, meaning it is below its book value. At first glance, we would say the second is the better option.

But here’s the problem. And it’s important that you understand it. The net book value only accounts for tangible assets. It does not consider brands, patents, software, or the talent of the team. That’s why tech companies almost always have very high P/B ratios. A software program costs little to develop but generates enormous value. If you only look at the net book value formula, you might think it’s overvalued, but you would be wrong.

Another issue is that the net book value depends on how the accountant does the numbers. There is something called creative accounting where you can legally manipulate results. You see nice books but the reality is different.

And the most famous case here in Spain is Bankia. It went public in 2011 with a 60% discount relative to its book value. It seemed like a bargain. But it turned out to be a total disaster. It was absorbed by Caixabank in 2021. That shows that net book value does not predict the future.

So, what is it really useful for? The net book value is useful as part of fundamental analysis, but never as the sole criterion. It helps you understand the accounting solidity of a company at a specific moment. But you need to look further: macroeconomic conditions, competitive advantages, management quality, future earnings prospects.

My recommendation is that you learn to calculate and understand this net book value formula, understand how the P/B ratio works, but never use it in isolation. Combine it with other analyses. It’s just another tool in your investment toolbox, not the magic solution. True opportunities arise when you do a comprehensive study and find companies with real advantages that the market still does not value correctly.