Some 40 per cent of those aged 46 to 55 are unaware of how much money they have saved in their pensions, Aviva found.
People in this age group are more likely than younger workers to have lost track of how much they have in their pension savings, with just 24 per cent of employees aged 22 to 30 saying they do not know how much they have put away.
The knowledge gap comes despite the launch of new pension freedoms in 2015 which give over-55s who have a defined contribution (DC) pension pot a wider range of options over how they can use their money.
Alistair McQueen, head of savings and retirement at Aviva, said: “Not knowing how much you have saved in your pension pots is like approaching retirement with a blindfold on.
“They can be accessed at age 55, at which point some big decisions might need to be made.
“Without knowing how much you have saved it’s difficult to put a plan in place that could improve your retirement.”
Under the pension freedoms, over-55s are no longer required to use their pension pots to buy an annuity retirement income.
They can now cash in their pot, take some of it, or leave it invested - or still buy an annuity if they want to.
There will also be tax implications to consider when people are weighing up their options.
The survey among more than 2,000 employees aged 22 to 65 found nearly a third - 31 per cent - across this age range admit to not knowing how much they have saved in their pensions.
Nearly half - 49 per cent - believe they need to be saving more.
Workers aged 31 to 45, many of whom will be dealing with the financial pressures of raising a family, are the most likely to say they need to increase their pension savings.
Across the survey, 42 per cent of workers feel secure, confident, proud or excited about their savings, a percentage nearly matched by the 41 per cent who feel worried, disappointed, stressed, regretful or panicked.
Women are much more likely than men to be worried about their savings levels, with 23 per cent of women saying this compared with 13 per cent of men.
Mr McQueen said: “For anyone who doesn’t know how much they have saved in their pension, now is the time to check.
“If you’ve had a few different jobs over the years then you may have money saved in different pension pots. If you don’t know the details of them then the Government’s pension tracing service is a good starting point.”
The Government said its recent reforms had “transformed pension saving in this country”.
A spokesman for the Department for Work and Pensions said: “Automatic enrolment has boosted the pensions prospects of almost 10 million people so far, setting them on the path to a financially secure retirement.
“We know there is more to do in terms of increasing contribution rates, and a further rise is due in April. The low numbers opting out of pension saving as we’ve introduced planned, gradual increases in contribution rates show our phased approach is the right one.”
Anyone seeking further information about pension savings can contact the Government’s free and impartial Pensions Advisory Service, Money Advice Service or for those approaching retirement, Pension Wise, the spokesman said.