Millions of UK adults aged 40-54 are underestimating how long they are likely to live by around a decade, leaving their financial security at risk in later life.
Research by Just Group has found that men of this age expect to live to 78.9 on average, despite government projections suggesting they are likely to live closer to 87.5.
Women in this 'Generation X' age bracket expect to live to 80.5 instead of the official forecast of 90.1, with Just Group communications director, Stephen Lowe, warning that underestimating could have "toxic consequences".
"Nearly a million members of Generation X are set to arrive at age 55 every year for the next decade or so, and will face crucial decisions about whether to take pension money or leave it to keep growing," he said.
"Without a realistic idea of how long they will need that pension fund to last, it will be difficult to make an informed decision - many people already seem to be making decisions their older selves are going to regret."
The research shows that life expectancies become more realistic as people get older, with the estimates of those over 70 not far off official projections.
It was found that men aged between 40 and 44 underestimate their life expectancy by approximately 12.1 years on average, but actually overestimate by half a year once they are 75-79 years old.
Similarly, women aged 40-44 predict they will live 10.4 years less than the government projections suggest, with this narrowing to 2.1 years once they are aged 75-79.
"The problem is that by then, it will often be too late because they made key choices many years earlier that may not be reversible," Lowe said.
"You can understand the temptation of taking cash out of the pension, but each pound taken early on might mean perhaps two pounds less a few years later when money is tighter."
Lowe went on to say that Generation X might be able to use their homes to counter this through equity release or downsizing, but that those approaching retirement should take advice before taking pension money.
"Longevity is unique in that it depends on a multitude of factors such as your own genes, health and lifestyle," he continued.
"People need to get more informed by taking the free and impartial government guidance from Pension Wise, or seeking professional advice, because bad decisions can have a huge effect on how comfortable you are in retirement."