Rambus Inc. (NASDAQ:RMBS) shareholders won't be pleased to see that the share price has had a very rough month, dropping 28% and undoing the prior period's positive performance. The drop over the last 30 days has capped off a tough year for shareholders, with the share price down 14% in that time.

In spite of the heavy fall in price, Rambus' price-to-earnings (or "P/E") ratio of 21.3x might still 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 17x and even P/E's below 10x are quite common. However, the P/E might be high for a reason and it requires further investigation to determine if it's justified.

Rambus certainly has been doing a good job lately as its earnings growth has been positive while most other companies have been seeing their earnings go backwards. The P/E is probably high because investors think the company will continue to navigate the broader market headwinds better than most. You'd really hope so, otherwise you're paying a pretty hefty price for no particular reason.

What Are Growth Metrics Telling Us About The High P/E?

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

Retrospectively, the last year delivered an exceptional 23% gain to the company's bottom line. Still, EPS has barely risen at all from three years ago in total, which is not ideal. Therefore, it's fair to say that earnings growth has been inconsistent recently for the company.

Turning to the outlook, the next three years should generate growth of 6.0% each year as estimated by the four analysts watching the company. With the market predicted to deliver 10% growth per annum, the company is positioned for a weaker earnings result.

With this information, we find it concerning that Rambus 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 this level of earnings growth is likely to weigh heavily on the share price eventually.

What We Can Learn From Rambus' P/E?

There's still some solid strength behind Rambus' P/E, if not its share price lately. While the price-to-earnings ratio shouldn't be the defining factor in whether you buy a stock or not, it's quite a capable barometer of earnings expectations.

We've established that Rambus currently trades on a much higher than expected P/E since its forecast growth is lower than the wider market. Right now we are increasingly uncomfortable with the high P/E as the predicted future earnings aren't likely to support such positive sentiment for long. Unless these conditions improve markedly, it's very challenging to accept these prices as being reasonable.

Before you take the next step, you should know about the 1 warning sign for Rambus that we have uncovered.

If these risks are making you reconsider your opinion on Rambus, explore our interactive list of high quality stocks to get an idea of what else is out there.

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