Some 3.6 million over-50s are unpaid carers, research by Saga Personal finance has found.
Of these, 792,000 have had to leave their job or change their hours to care for loved ones, seeing their own income fall.
The financial cost to unpaid carers is an average of £170 a month, making an overall bill of £612m, not including the cost of the reduction in their income.
Adaptions to the home are also common with further costs, an electric stairlift can cost around £3,000, while a walk-in bath can cost up to £4,000.
The results came from a Populus poll of 9,794 Saga customers aged over 50, and was conducted online in September.
Charities have warned that many patients with conditions such as dementia are reliant upon unpaid carers for daily living, as part of a warning over the state of health and social care.
Jeff Bromage, chief operating officer at Saga Personal Finance, commented: "Unpaid family carers do so much good for other people and society as a whole. In doing so, many don't count the cost to their own pocket or health. They are the glue that holds our caring society together.
"Saga is calling for extra help for those that can't afford vital home adaptations, which can be vital for the quality of life of both the carer and the person receiving care."