The NSL Ltd (SGX:N02) share price has done very well over the last month, posting an excellent gain of 37%. Looking back a bit further, it's encouraging to see the stock is up 31% in the last year.

Since its price has surged higher, NSL may be sending very bearish signals at the moment with a price-to-earnings (or "P/E") ratio of 34.8x, since almost half of all companies in Singapore have P/E ratios under 13x and even P/E's lower than 7x are not unusual. However, the P/E might be quite high for a reason and it requires further investigation to determine if it's justified.

As an illustration, earnings have deteriorated at NSL over the last year, which is not ideal at all. It might be that many expect the company to still outplay most other companies over the coming period, which has kept the P/E from collapsing. If not, then existing shareholders may be quite nervous about the viability of the share price.

View our latest analysis for NSL

How Is NSL's Growth Trending?

There's an inherent assumption that a company should far outperform the market for P/E ratios like NSL's to be considered reasonable.

If we review the last year of earnings, dishearteningly the company's profits fell to the tune of 17%. This has erased any of its gains during the last three years, with practically no change in EPS being achieved in total. So it appears to us that the company has had a mixed result in terms of growing earnings over that time.

Weighing that recent medium-term earnings trajectory against the broader market's one-year forecast for expansion of 8.9% shows it's noticeably less attractive on an annualised basis.

In light of this, it's alarming that NSL's P/E sits above the majority of other companies. Apparently many investors in the company are way more bullish than recent times would indicate and aren't willing to let go of their stock at any price. Only the boldest would assume these prices are sustainable as a continuation of recent earnings trends is likely to weigh heavily on the share price eventually.

The Bottom Line On NSL's P/E

NSL's P/E is flying high just like its stock has during the last month. 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.

We've established that NSL currently trades on a much higher than expected P/E since its recent three-year growth is lower than the wider market forecast. 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.

You always need to take note of risks, for example - NSL has 4 warning signs we think you should be aware of.

It's important to make sure you look for a great company, not just the first idea you come across. So take a peek at this free list of interesting companies with strong recent earnings growth (and 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.