A quarter of UK adults aged 55-64 surveyed by Standard Life who are still working said they are only budgeting for their retirement income to last 10 years or less, despite an average life expectancy of 82 years.
Just over one in ten (12%) said they were only planning for their retirement income to support them for one to five years.
Almost a third (29%) of over-55s still working expected to need the same amount of money each year throughout their retirement.
However, 27% were not sure of their retirement income needs and how they will change over the years.
Women were more unsure than men of their annual income needs in retirement, with 31% reporting uncertainty around future income requirements, compared to 22% of men.
Despite the uncertainty about future financial requirements among those nearing retirement age, the research also found that 80% of over 55s have not sought financial advice in relation to their retirement income needs, with 46% having no intention to do so in the future.
A separate report released today by protection provider Vitality said advisers consider the biggest threat on the horizon to people drawing down their pensions appropriately is them underestimating their own life expectancy. Vitality surveyed 202 advisers in February.
Mike LeGassick, director at Financial Planning firm Manning and Company, said: "Having conversations with our clients about what their long-term financial goals are is absolutely key – and life expectancy is an integral part of this.
"Time and time again we hear that clients aren’t taking into consideration what their retirement might look like in older age and with life expectancy increasing, this is a real concern."