Millions of people are underestimating the cost of paying for a care home by an average of £12,000 a year, a survey suggests.
Which? found that 55% of people estimated a figure for the cost of a private nursing home place in their area that fell short of the average cost.
On average, people underestimated the true cost of a care home place in England by £237 per week - the equivalent of £12,000 a year.
One in 10 people underestimated the true cost by more than £757 per week - the equivalent of £39,000 a year - while a quarter gave a figure that was too low by more than £507 per week, the equivalent of £26,000 a year.
Three in 10 people said they did not know the weekly cost of a nursing home in their region, while just 15% got the answer right or overestimated the cost.
Londoners had the most unrealistic expectations overall, underestimating the cost of a nursing home place by an average of £540 a week - the equivalent of £28,080 a year.
There are more than 400,000 people in the UK living in residential and nursing care homes. Of these, almost half pay for care themselves and the rest are paid for, either wholly or partly, by their local authority or the NHS.
Previous Which? research found that just one in 10 adults aged 55 or over say they have put money aside to pay for care needs as they get older.
Which? managing director of public markets, Alex Hayman (pictured), said: "Many people are seriously underestimating the costs of care in later life, meaning they could struggle to find high-quality care for themselves or a loved one, or even face financial difficulties.
"The care system can be confusing and daunting and must often be navigated at a time of great stress for older people and their families. That's why it's vital that people have access to tools and resources to help them plan for the future."
Which? has launched an online tool to help families get information about the likely cost of care in their local authority area in England.
Ian Hudspeth, chairman of the Local Government Authority's Community Wellbeing Board, said: "Our recent polling shows half of people have little or no understanding of what social care means. Only 15% of people polled said they are making plans to pay for their care in later life, so it is no wonder people underestimate the cost.
"With low public awareness of social care and people's preparedness for how to pay for it, it is more important than ever that the Government get on and publish their green paper, start a massive campaign to raise awareness of what social care is and don't duck the big issues on funding."
Populus surveyed 2,074 UK adults on behalf of Which? in May.
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