I've seen many people ask about stock prices being too high or too low lately. I think some still don't understand what the P/E ratio really is, and it's a pretty important tool when choosing stocks wisely.

Simply put, the P/E or Price-to-Earnings ratio is about comparing the stock price to the company's earnings. Basically, it tells you how many years you'd need to wait to break even if you buy the stock at this price, assuming the company’s profit remains the same every year.

Calculating the P/E isn't complicated. Just divide the current stock price by the EPS (Earnings Per Share). The lower the P/E, the cheaper the stock and the faster you can recoup your investment. For example, if a stock costs 5 baht and has an EPS of 0.5 baht, the P/E would be 10 times, meaning you'd need 10 years to break even.

What’s interesting is that there are two types of P/E: Forward P/E, which uses the current price divided by expected future earnings, and Trailing P/E, which uses actual earnings from the past 12 months. Trailing P/E is more popular because it’s based on real data, but Forward P/E can give a picture of future growth, though it involves some risk since it’s an estimate.

However, you should be cautious because P/E isn’t a perfect tool. EPS isn’t constant; if the company grows or faces problems, EPS will change, and so will the P/E. For example, if a company successfully expands and EPS rises to 1 baht, the P/E drops to 5, meaning a faster return. Conversely, if there’s an issue like trade restrictions and EPS drops to 0.25 baht, the P/E jumps to 20, indicating a longer wait.

In summary, the P/E ratio is a useful tool to assess whether a stock is cheap or expensive, but it shouldn’t be relied on alone. It’s best to study it alongside other tools, and most importantly, consider the company's future profit prospects. Good investing looks ahead, not just at the past.