Some parts of the UK have seen the number of people diagnosed with dementia more than double in five years, analysis of NHS data shows.
A drive to increase diagnosis rates and an ageing population were behind the increase, experts said.
Charities said dementia care provision must improve, calling it a "ridiculous lottery", and "very hit or miss".
NHS England said it was a priority to diagnose dementia earlier so people could receive correct treatment.
Across England, Wales and Northern Ireland, the number of people on the register has risen by 40% to around 508,000.
Scottish health officials estimate there are a further 90,000 people living with dementia north of the border.
'Care cost £100k'
Kerry Hillier, 41, of Sutton Coldfield, West Midlands, said her family had spent "in the region of £100,000" over 10 years to top up direct NHS payments to cover her mother's care costs, and that "did not include food and accommodation". She was diagnosed with dementia in 2009.
She said: "When she was diagnosed, it was very much denial on her part.
"We wanted to care for her at home and felt that she would be less agitated if she didn't go to a care home.
"Funding that we got from direct payments from the NHS was very small.
"It equated to a few hours per day, and we were paying the carer around £9 or £10 per hour at that stage. We had to top it up with pensions and savings.
"I really felt that the whole system was very unfair and weighted against us."
Sue Kerfoot's father Roy went into a private care nursing home in June 2015 for physical disabilities before his dementia diagnosis, costing him about £50,000 per year.
Mrs Kerfoot, who lives in rural Derbyshire, said: "This was not an expensive place.
"That was par for the course, and not top of the range.
"A state pension would never cover the financial element that you need for this."
Psychologist Mrs Kerfoot thought a community support network could help provide the care a lot of dementia sufferers need.
As of March this year, about 1% of the populations of England, Wales and Northern Ireland were on their dementia registers.
Studies, however, suggest there are many people with dementia who have not yet been diagnosed.
Across the UK
- In England, places where the number of people on the register has more than doubled from 2014 to 2019 include Surrey, Lincolnshire, Bexley in south-east London, and parts of Kent including Canterbury, Dartford and Gravesham
- In Ayrshire and Arran in Scotland, the number of people diagnosed with dementia increased by a third, according to Scottish government estimates
- A similar increase in diagnoses took place in the Western Local Commissioning Group in Northern Ireland, which covers the five council areas of Limavady, Londonderry, Strabane, Omagh and Fermanagh
- In Abertawe Bro Morgannwg in Wales - now known as Swansea Bay University Health Board - there was a 29% increase.
Prof Sube Banerjee, from Plymouth University's Faculty of Health, said there had been a target by NHS England to increase diagnoses.
"Ten years ago, only a third of people with dementia were diagnosed, and when they were it was late in the illness when it was too late to help them make choices about treatment."
He said he believed a target diagnosis rate of 67% set in the National Dementia Strategy had now "been achieved".
Who pays for care?
Anyone with savings or income above £23,250 is expected to pay for their own care fees.
People with savings below that are entitled to help with the cost of care from their local council. Generally, the less savings the person has, the more the authority will pay towards care.
This money goes towards paying for a carer to visit, or for a care or nursing home.
The current standard amount the NHS will pay towards nursing care is £165.56 per week, according to the Alzheimer's Society.
As funding is linked to an individual's means, health services which may also help - such as hospitals - do not necessarily receive more public money if more people with the condition live in any one area.
A report from the London School of Economics shows the cost of dementia to the UK economy is £34.7bn per year.
Dr Karen Harrison-Dening, head of research and publications at Dementia UK, said there was no standardised service across the country.
"Care at the moment is very hit or miss. We rely heavily on families to care for their loved ones themselves," she said.
"If you developed cancer in later life the NHS would step in.
"There would be NHS Continuing Healthcare, Macmillan nurses and bereavement support, but far less likely in dementia."
Ewan Russell, from the Alzheimer's Society, said: "Often the support simply is not there and when it is there, it is often poor quality.
"It is heartbreaking and not right that people with dementia have to battle to get the care that they need.
"The government has to step in and boost people's support. It is a ridiculous lottery that people with dementia can lose their homes and savings and that has to end."
NHS England said it was "good news" that "thanks to concerted efforts nationally and locally" more people had been diagnosed with the disease. It said early diagnosis and treatment was a "top priority".
English local government spending on adult social care rose by 11% in the same period, the BBC Shared Data Unit found.
Meanwhile, from 2016 to 2019, NHS England increased its spending on dementia care by 18%.
More about this story
The Shared Data Unit makes data journalism available to news organisations across the media industry, as part of a partnership between the BBC and the News Media Association. This piece of content was produced by a local newspaper journalist working alongside BBC staff.