CSP Inc. (NASDAQ:CSPI) shareholders would be excited to see that the share price has had a great month, posting a 38% gain and recovering from prior weakness. The last month tops off a massive increase of 138% in the last year.

After such a large jump in price, CSP's price-to-earnings (or "P/E") ratio of 27.8x might make it look like a strong sell right now compared to the market in the United States, where around half of the companies have P/E ratios below 16x and even P/E's below 9x are quite common. Although, it's not wise to just take the P/E at face value as there may be an explanation why it's so lofty.

CSP certainly has been doing a great job lately as it's been growing earnings at a really rapid pace. It seems that many are expecting the strong earnings performance to beat most other companies over the coming period, which has increased investors' willingness to pay up for the stock. If not, then existing shareholders might be a little nervous about the viability of the share price.

How Is CSP's Growth Trending?

CSP's P/E ratio would be typical for a company that's expected to deliver very strong growth, and importantly, perform much better than the market.

If we review the last year of earnings growth, the company posted a terrific increase of 166%. Still, EPS has barely risen at all from three years ago in total, which is not ideal. Accordingly, shareholders probably wouldn't have been overly satisfied with the unstable medium-term growth rates.

Weighing that recent medium-term earnings trajectory against the broader market's one-year forecast for expansion of 13% shows it's noticeably less attractive on an annualised basis.

With this information, we find it concerning that CSP is trading at a P/E higher than the market. It seems most investors are ignoring the fairly limited recent growth rates and are hoping for a turnaround in the company's business prospects. There's a good chance existing shareholders are setting themselves up for future disappointment if the P/E falls to levels more in line with recent growth rates.

The Bottom Line On CSP's P/E

The strong share price surge has got CSP's P/E rushing to great heights as well. Generally, our preference is to limit the use of the price-to-earnings ratio to establishing what the market thinks about the overall health of a company.

Our examination of CSP revealed its three-year earnings trends aren't impacting its high P/E anywhere near as much as we would have predicted, given they look worse than current market expectations. When we see weak earnings with slower than market growth, we suspect the share price is at risk of declining, sending the high P/E lower. If recent medium-term earnings trends continue, it will place shareholders' investments at significant risk and potential investors in danger of paying an excessive premium.

Don't forget that there may be other risks. For instance, we've identified 1 warning sign for CSP that you should be aware of.

If you're unsure about the strength of CSP's business, why not explore our interactive list of stocks with solid business fundamentals for some other companies you may have missed.

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This article by Simply Wall St is general in nature. We provide commentary based on historical data and analyst forecasts only using an unbiased methodology and our articles are not intended to be financial advice. It does not constitute a recommendation to buy or sell any stock, and does not take account of your objectives, or your financial situation. We aim to bring you long-term focused analysis driven by fundamental data. Note that our analysis may not factor in the latest price-sensitive company announcements or qualitative material. Simply Wall St has no position in any stocks mentioned.