One of the most often-repeated investing mantras says ‘sell in May and go away, don’t come back until St Leger Day’, referring to a well-known British horse racing day which takes place in September.
The saying may date back as far as the 18th century, and at least to a 1950s edition of Stock Trader's Almanac. In those days, financial professionals would typically spend most of the summer on holiday. The issue wasn’t so much that stocks would fall over the summer, but that they wouldn’t do a whole lot at all.
“The rationale is simply that, back in the mists of time, the main market participants (think bowler hats and coffee shops in London) were all away on their summer holidays and socials,” said Ben Seager-Scott, CIO at advisory firm Forvis Mazars. “There simply wasn’t much of a market and everything, at best, drifted until everyone came back after the summer.”
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But does this stock market saying hold any value for your investments today?
The short answer appears to be no.
“There is scant evidence that it was true historically and I think there’s even less of a case now, with constant 24-hour news cycles, much wider market participation and ubiquitous mobile communication technology,” said Seager-Scott.
Did ‘sell in May’ work in 2025?
While the adage often fails to deliver, it rarely performs as badly as it did last year.
Major indices enjoyed encouraging returns between May and September, largely reflecting an uptick in investor sentiment following the chaotic fallout from Trump’s Liberation Day tariffs, announced on 2 April.
“Last year was a great example of when [selling in May] would not have worked out in your favour,” said Adrian Murphy, CEO of wealth manager Murphy Wealth. “Had you done so, you would have missed out on a good deal of the recovery from the tariff shocks in April – the S&P 500 rose more than 18% and the FTSE 100 gained more than 9% from May to mid-September
And the geopolitical tensions plaguing the market this year could be just as much of a reason to avoid selling in May in 2026 as they were last year.
“With the conflict in the Middle East, markets are volatile,” said Murphy. “No one knows how the situation will pan out in the short term, let alone the next few months and beyond.
“You are as likely to crystallise any losses and be forced to reinvest at a higher price at the end of the summer, as you are to make gains by buying back in again when the market looks cheaper,” Murphy added.
However, there is some evidence that trading volumes are lower over the summer and during the Christmas period. That can increase market volatility, because fewer buyers and sellers can necessitate larger jumps between prices in order to buy or sell a stock.
“But this is very much two-way,” said Seager-Scott. That extra volatility can push prices up or down, depending on sentiment.
“That may partly explain the Santa rally effect,” Seager-Scott said, adding that there is little evidence that this is a seasonal pattern and rather a label that is applied in hindsight whenever markets happen to rise in December.
It’s questionable whether or not there’s any empirical evidence to support selling your shares in May. Various studies have looked into the results, and between them they paint a fairly blurred picture.
Fidelity International, for example, found that selling stocks in May generated positive returns in just 14 of the last 38 years. Investopedia investigated the trend going back to the 1930s and while it found that summers have generally yielded higher returns than winter since the 1950s, the opposite was true for the two decades before then.
Analysis from investing platform IG has found that years when Trump is in office have completely subverted the traditional ‘sell in May’ mantra.
The analysis found that the S&P 500 has returned 9.5% between May and October during Trump years, vs 1.3% during non-Trump years over the past two decades. That said, Trump years have also seen better-than-average performance for the index across the full year, with average annual gains of 14.6% in Trump years compared to 6.8% in non-Trump years.
“While Trump-specific trading patterns have already emerged, most notably the TACO [‘Trump Always Chickens Out’] trade of buying the dip before Trump’s key trade and foreign policy deadlines, investors in US equities should also be reconsidering their summer trading habits,” said Chris Beauchamp, chief market analyst UK at IG. “We may yet see a ‘Summer of Trump’ trend emerge as investors cotton on.”
The FTSE 100, though, tends to fare worse between May and October when Trump is in power compared to years when he isn’t. The index fell 2% on average over the summer months in years when Trump was in power, compared to gaining 0.6% in non-Trump years over the last 20.
On the face of it, that might seem to suggest that if you are invested in UK stocks it could make sense to sell in May, at least when Trump is in power, but on the whole most investment experts don’t think this is a good idea.
“In terms of good investment practice, given that markets tend to rise over time and, importantly, dividend income also accrues through the year, I’m not convinced opting to be sat in cash half the time makes much sense to me,” said Seager-Scott.
On that basis, time in the market, rather than timing the market, seems to be the more reliable (and easier) strategy.
