Is the S&P 500’s growth sustainable? Here’s what UK investors should watch

The S&P 500 hit a new record high of 7,168 points last Friday (24 April). That’s a 13% increase in just April alone, after the index dipped to 6,343 points on 30 March.

The rapid growth has raised concerns over sustainability amid the backdrop of the Iran war. A small group of major tech stocks are driving the growth, many of which are publishing results this week.

Alphabet, Microsoft, Amazon (NASDAQ: AMZN) and Meta are all scheduled to report earnings on Wednesday with Apple reporting the following day.

So the question is: will their performances validate the growth, or could it all be a house of cards?

Heavy concentration

With a combined value of around $16trn, these five tech giants make up approximately one-quarter of the entire S&P 500’s market capitalisation.

So it’s fair to say we could be in for a volatile week. Even if just one of the companies falls short of expectations, it could have a significant impact on the market.

FactSet says the S&P 500 is on track for about 15.1% year-on-year earnings growth for Q1 2026, while the Information Technology sector is expected to be the main driver of that expansion.

Naturally, upbeat guidance would keep the growth picture intact and could push estimates higher.

But what could go wrong?

Identifying weakness

Out of the five, Amazon looks the most vulnerable to missing expectations. The main reason is that recent commentary flags stagnant revenue trends, rising spending, and the possibility that operating income could even contract.

That makes it feel a bit more fragile than the others.

That said, the company’s recent results hardly look disappointing.

Let’s take a quick look at some numbers:

• Fourth quarter net sales: up 14% to $213.4bn.
• Annual 2025 revenue: $716.9bn (up from $638bn in 2024).
• Full-year operating income: $80bn in 2025 (versus $68.6bn in 2024).

These numbers suggest that profitability is still improving alongside scale. That back’s the narrative that Amazon remains an appealing US tech stock to consider in the long run.

So what’s the concern?

Execution risk

What matters is that Amazon has been spending heavily on logistics, cloud infrastructure, and AI-related capex.

So now investors are watching whether those investments keep converting into meaningful cash flow.

Risk-wise, if AWS growth slows, retail margins weaken, or AI capex fails to translate into better returns, the market could punish the stock quickly.

So the biggest risks are execution and valuation.

The bottom line

The market’s reaction this week will probably depend as much on guidance as on the headline numbers. At these high valuations, investors are paying for sustained growth, not just a one-quarter pop.

So, even if they report well but guide conservatively, the S&P 500 could still struggle to extend gains.

What does this mean for UK investors?

Even for those without significant US exposure, the knock-on effect could cause volatility within the UK market.

Having a highly diversified portfolio supported by defensive shares can help reduce risk. A few popular options on the FTSE 100 include GSK, AstraZeneca, and National Grid.

But it’s a constantly evolving market, so keeping abreast of developments is key to good portfolio management.

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