Which? has been using Freedom of Information requests over the last five years to ask councils across England and Wales what level of home care they provide.
More than four-fifths (80%) of councils which responded in the latest survey now restrict care to those whose needs are "critical" or "substantial", up from just over 70% when similar research was carried out in 2009.
Someone's needs are deemed to be critical if there is a potential threat to life, they have significant health problems or are unable to carry out vital everyday tasks like washing or dressing.
If their needs are termed substantial, this means they are unable to perform most everyday routines or have little support.
Around one third of 100 councils which responded about their care charges in both 2009 and 2013 have increased these above the rate of inflation and some local authorities have either scrapped weekly caps that limit how much people have to pay, or raised the level of the cap so they have to pay more, Which? said.
With varying changes in eligibility and care costs, Which? is urging the Government to make sure elderly people and their families get better information and advice about the care they are entitled to and how much they will need to pay.
Which? wants councils to provide information that is tailored to individual situations, and targeted at key "pinch points", for example when people see their GP or are discharged from hospital.
Which? executive director Richard Lloyd said: "Our research starkly exposes the postcode lottery of home care provision.
"With limited resources and changes being introduced through the Care Bill, it has never been more important for people to get the best possible advice and information about the help they can expect.
"We want to see greater transparency from local authorities over the provision of care and greater consistency in the way they charge."
Some 152 councils responded to the Which? survey this year.
Care and Support Minister Norman Lamb said: "We know people are often confused about what care they can expect from their local authority and far too many end up having to fight for the care that they need because the rules are so complicated.
"That is why we are introducing new national eligibility criteria in 2015 that will set a minimum threshold that will allow local authorities to keep current levels of access to care and support.
"In my view, we need to be clear about the basic minimum entitlements to services so that everyone can be reassured there is some level of support they can expect, regardless of where they live.
"A national minimum is exactly that - a starting point for local councils to base their care provision on.
"We are also starting work on a new approach to eligibility - which aims to offer some help to families earlier on to help prevent a deterioration of condition."