The study, commissioned by the Continuing Care Conference and Age Concern, shows that finding residential care, or care at home, in old age often depends on where people live rather than what they need.
Researchers found that eligibility criteria for allocating care can be unsound and vary widely. Rules are not always interpreted consistently or linked to the allocation of resources, says the study.
Sally Greengross, director-general of Age Concern, said: "Long-term care for older people is a national lottery. It's unacceptable that getting the care you need in old age is down to the luck of the draw.
Eighty-three social services departments from England took part in a survey conducted by the Personal Social Services Research Unit at the University of Manchester.