One in seven people planning to retire this year has no private pension to fall back on and many will be forced to get by in poverty, an insurer has warned.
Women who are set to retire in 2013 were nearly three times more likely than men to be relying on the state as their sole form of pension income, Prudential found.
Many can expect financial difficulties in retirement
Some 14% of this year's retirees said they had no company or personal pension and their only form of pension income would come from the state.
The full basic state pension is currently set at £110.15 a week, but how much someone receives depends on how many years of contributions they have made.
Almost one quarter (23%) of women will be retiring this year without a private pension, compared with just 8% of men, according to the survey .
Nearly one-fifth of those planning to retire this year will be living below the poverty line, Prudential's analysis suggested.
Some 18% of people surveyed will be living on less than £8,254 a year, which is the amount estimated by the Joseph Rowntree Foundation that a single pensioner in the UK needs to live on.
The state pension will account for an estimated 43% of the average retirement income for women in 2013, while the average man retiring this year will receive 30% of his income from the state.
But Prudential found that almost one quarter (23%) of people retiring this year overestimated the amount the state pension paid by more than £600 a year.
One in 10 people surveyed had "no idea" how much the state pension paid.
The findings come amid a landmark overhaul of the pensions landscape, to tackle the savings crisis of people living for longer but failing to put enough cash aside for their later years.
The government is rolling out the automatic enrolment of millions of people into workplace pensions in a staging process which began with larger firms.
Reforms to the state pension are also in the pipeline, amid general moves to make pension saving easier for people to understand and fairer.
The government is scrapping the two-tier system of basic pension and earnings-related additional pension from 2016, which will mean a single flat rate of around £7,000 a year - or £144 a week, in today's money.
Vince Smith-Hughes, retirement income expert at Prudential, said: "The basic state pension alone is not nearly enough to provide a comfortable standard of living.
"While it's a very valuable source of additional income for millions of pensioners, the state pension should ideally only represent a part of someone's retirement income, not all of it.
"Relying on the state will see many people retiring below the poverty line this year, which shows the importance of building up a personal pension."
The findings also come at a time when older people with savings are facing a struggle to make any real returns on their cash.
The number of accounts on the market which offer savers inflation-beating returns has plummeted from over 150 a year ago to seven, according to financial information website Moneyfacts.
More than 1,000 people who plan to retire this year took part in Prudential's research.
Joanne Segars, chief executive of the National Association of Pension Funds (NAPF), said: "The average man or woman retiring now is expected to live into their 80s, and lifespans are increasing every year.
"It is worrying that around 100,000 people face the grim prospect of spending their final two decades struggling to get by on the state pension alone, and even more will be below the poverty line.
"Our state pension is up for some long overdue reform to make it simpler and fairer, and auto-enrolment will bring millions of people into a workplace pension.
"These vital changes will tackle the problem for future generations, and also help narrow the gender divide, but sadly they will come too late for this year's pensioners."