The GMB Union has estimated that 90% of those who go into care will die before they reach the £72,000 Dilnot cap on the costs of care.
The cap does not apply to top-up fees and "hotel-costs" such as food and other costs related to accommodation.
The GMB calculated the average resident will take 4 years and 9 months to reach the cap, which comes into force in April 2016.
It said allowing for mortality in care rates there is around a 1 in 10 chance of reaching the cap before death.
Those in London will be most likely to live long enough to reach the cap with it taking 3 years and 2 months to reach it while in the North West of England it will take 5 years and 9 months.
The national average time to reach the cap is 4 years and 9 months, compared to an average stay in care of 2 years and three months.
The longest-staying 25% of people are in care for 3 years and 4 months in care while the longest staying 10% are in care for an average of around 5 years and 10 months.
The GMB's figures came from Bupa.
Justin Bowden, GMB national officer, said: "The complete inadequacy of the government's cap on eligible care fees is laid bare for all to see.
He continued: "This is a betrayal of hundreds of thousands of citizens who contributed to this country all their working lives and were promised a cradle to grave system of care would be there if they needed it, free at the point of use.
"Instead they are thrown into a lottery whose outcome depends on whether or not they are one from twenty from each age group who will need to go into a care home and if so how long they will be there.
"At their most vulnerable and needy, they are expected to empty their hard earned savings or sell their houses long before reaching the cap.
Bowden called for an end to means-testing and caps saying: "The Westminster parties should make manifesto pledges to integrate elderly care with the health service and fund both from general taxation. This would patently be a fairer system.
"Older people are being short-changed by the current approach to funding. The care workforce is getting a raw deal too. The sector desperately needs more public investment and control."
