Rolls-Royce (LSE: RR.) shares have delivered underwhelming returns over the last eight months. While other growth stocks like Nvidia, AMD, and Alphabet are up 20%+, the engine maker’s stock is basically flat.

So, what’s going on here? And are the shares still worth considering for an ISA or SIPP?

The environment has changed

The reason the shares have underperformed is pretty simple. The operating environment has changed…dramatically.

While Rolls-Royce is a diversified company today, it still generates a large proportion of its revenues from the servicing of aircraft engines (these are measured in flying hours). And with oil prices at high levels due to the conflict in the Middle East, the world’s airlines are cutting back on flights, meaning that there’s some uncertainty over flying hours.

This change in the backdrop is likely to hamper Rolls-Royce’s performance in the near term. I don’t think results in 2026 are going to be a disaster (the group has said that the change in backdrop is manageable), but they most likely won’t be as strong as they might have been if oil was still at $60-$70 per barrel as it was at the start of the year.

For example, in the company’s H1 results, the group may not raise its profit guidance like it has on multiple occasions in recent years. Performance could be more in line with expectations (or perhaps slightly worse).

A pause for breath

You could also argue that a period of share price consolidation was due here. After all, between the start of 2023 and late 2025, the shares rose by over 1,000%.

No stock continues rising in a straight line forever. At some point, there is always a period of consolidation where previous gains are digested and fundamentals catch up with valuations (note that the valuation here remains quite high).

No longer a momentum play

Another factor could be the momentum breakdown. These days, there are a lot of funds (and investors) that track share price momentum and invest in high momentum stocks (giving these stocks an added boost).

Given that the upward trend in the share price has broken down recently, the stock now has less appeal from a momentum investing perspective. This could be contributing to the underperformance.

Worth a look today?

Are the shares worth considering today? Well, they could be – there’s certainly less hype around them and I see that as a good thing.

That said, I think it could pay to wait. I’m still convinced that we might see better buying opportunities in the months ahead.

Personally, I have a hunch that the shares are going to fall back to near 1,000p. This hunch is based on a combination of fundamentals (ie, the changing operating environment) and technicals (the deteriorating share price momentum).

If they were to fall back to this level, I think it could be a good opportunity to consider. Because, in the long run, this company has plenty of growth potential given its exposure to defence and nuclear energy.

Should you invest £5,000 in Rolls-Royce Plc right now?

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Edward Sheldon has positions in Nvidia and Alphabet.