Pensioners could still face huge bills for residential care despite the Government's plan to cap costs at £72,000, according to Labour calculations.
The Government's cap does not cover accommodation and living expenses, and care costs only count towards the limit at the rate the local council would pay for a place in a residential home.
Labour analysis showed that as a result it will take almost five years for elderly people to hit the cap - during which time they will have clocked up more than £150,000 for their actual residential care home bill.
In 2016/17 when the cap is due to come into effect the av erage council rate for residential care is estimated to be £522 a week, but the average price of a care home bed will be £610 a week.
The difference between the council rate and what pensioners actually pay will not count towards the cap.
Pensioners in care homes will also have to pay £230 a week for their accommodation, which is counted separately from care costs and does not count towards the cap.
The Daily Telegraph reported that in some areas of the country with higher average care home costs, people could face paying more than £500,000 before the cap was reached.
In parts of Surrey a bed in a standard residential care home typically costs around £800 a week, but local council rates are around £326 a week, the newspaper reported.
The difference would mean a resident must spend more than £560,000 over 12 years before seeing costs capped.
Labour also estimated that six out of seven elderly people will have died before they reach the cap.
Shadow minister for care and older people L iz Kendall said: "David Cameron has repeatedly claimed that no-one will have to pay more than £72,000 to pay for their care, but this simply isn't the case.
"On average, pensioners will have to pay more than twice this amount, and the vast majority will have died before they hit the so-called 'cap'.
"David Cameron should be straight with elderly people about what they will really have to pay for their care. Families deserve to be told the facts, rather than being conned, so they can properly plan for the future, and not have the Government attempt to pull the wool over their eyes."
But health minister Norman Lamb hit out at Labour's inaction on tackling the problem of crippling care costs while they were in power.
The care and support minister said: "It's rank hypocrisy for Labour to criticise the coalition's care cap when they did nothing to fix an unfair social care system in 13 years of plenty.
"At the same time as dealing with Labour's debts, we have gone further than they ever did and found £2 billion to cap care costs and end the scandal of people being forced to sell their home in their lifetime to pay for care.
"Of course we would love to be able to afford to go further, but we won't take any lectures from the party who racked up a record budget deficit and forced old people to sell their homes to pay for care."