The funding gap for reforming social care in England could be plugged by raiding the NHS surplus or restricting access to benefits such as the winter fuel allowance, experts say.
A review published last year suggested care costs should be capped, but this would cost an extra £1.7bn a year.
The Nuffield Trust analysis believes this sum could be found from within existing public sector spending.
The think-tank said tax rises could be used too.
But it questioned whether that would be appropriate in the current financial climate and said if they were to be introduced they should be targeted at elderly people.
The report comes as the government is still finalising its plans for reforming the way people pay for care in their own homes and in care homes.
A White Paper is expected to be published next month.
One of the proposals under consideration is the idea of introducing a cap on lifetime care costs of between £35,000 and £50,000.
This was put forward by the Dilnot Commission, which was set up by the government to look into the issue.
Funding is the most controversial element of the changes, with the Treasury thought to have concerns about the cost to the public purse of reforming the system.
By 2026, the estimated additional annual cost of £1.7bn is likely to rise to £3.6bn because of the ageing population.
But the Nuffield Trust said it was feasible to look at redistributing current spending to cover the bill.
It pointed out that about £140bn a year is spent on elderly people across the NHS, welfare and social care sectors.
Just 6% of this currently goes on social care.
The Nuffield Trust said the extra cost could be plugged through a variety of measures.
For example, it cited a £1.5bn underspend in the NHS last year.
Money could also be saved by means-testing benefits such as winter fuel payments, travel concessions and free TV licences.
Report author Anita Charlesworth said it was important that the government had an open debate with the public about priorities.
"The government currently spends some £140bn a year on older people.
"If you were starting with a blank sheet of paper is this the best balance of spending to ensure quality of life, dignity and respect in older age?"
Michelle Mitchell, of Age UK, agreed, saying an "honest debate" was needed and she urged ministers to have "courage and conviction" in their attempts to reform the system.
The government said it would be publishing its plans soon.