Marten Transport, Ltd.'s (NASDAQ:MRTN) price-to-earnings (or "P/E") ratio of 20.5x might make it look like a 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. Nonetheless, we'd need to dig a little deeper to determine if there is a rational basis for the elevated P/E.

Marten Transport could be doing better as its earnings have been going backwards lately while most other companies have been seeing positive earnings growth. It might be that many expect the dour earnings performance to recover substantially, which has kept the P/E from collapsing. If not, then existing shareholders may be extremely nervous about the viability of the share price.

View our latest analysis for Marten Transport

Does Growth Match The High P/E?

The only time you'd be truly comfortable seeing a P/E as high as Marten Transport's is when the company's growth is on track to outshine the market.

If we review the last year of earnings, dishearteningly the company's profits fell to the tune of 23%. This has soured the latest three-year period, which nevertheless managed to deliver a decent 29% overall rise in EPS. Accordingly, while they would have preferred to keep the run going, shareholders would be roughly satisfied with the medium-term rates of earnings growth.

Shifting to the future, estimates from the dual analysts covering the company suggest earnings growth is heading into negative territory, declining 0.7% over the next year. Meanwhile, the broader market is forecast to expand by 10%, which paints a poor picture.

With this information, we find it concerning that Marten Transport is trading at a P/E higher than the market. It seems most investors are hoping for a turnaround in the company's business prospects, but the analyst cohort is not so confident this will happen. Only the boldest would assume these prices are sustainable as these declining earnings are likely to weigh heavily on the share price eventually.

The Final Word

Using the price-to-earnings ratio alone to determine if you should sell your stock isn't sensible, however it can be a practical guide to the company's future prospects.

We've established that Marten Transport currently trades on a much higher than expected P/E for a company whose earnings are forecast to decline. When we see a poor outlook with earnings heading backwards, we suspect the share price is at risk of declining, sending the high P/E lower. This places shareholders' investments at significant risk and potential investors in danger of paying an excessive premium.

Plus, you should also learn about this 1 warning sign we've spotted with Marten Transport.

Of course, you might find a fantastic investment by looking at a few good candidates. So take a peek at this free list of companies with a strong growth track record, trading on a low P/E.

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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.