Hundreds of families say they have had to wait months or even years for a dementia diagnosis for a loved one.
Such long delays have an impact on their own work, finances and mental health, a survey for the Alzheimer's Society charity reveals.
The charity is calling for a national standard that would mean someone with dementia would receive an accurate diagnosis within 18 weeks of being seen and referred by a GP.
That would put dementia on a similar footing as other major health conditions, including cancer.
Michael Fethon says his dad, Jim, waited 18 months from their initial appointment with a GP before being diagnosed.
It was a delay that took its toll on Jim - and on Michael, who eventually had to give up his job to care for his dad.
"I think my dad felt beside himself because he was experiencing symptoms. It wasn't just memory loss."
Michael says his father struggled to drive, shop and, eventually, even to walk.
"It almost spiralled in that 18 months of his condition, gradually getting worse.
"If we'd have had a diagnosis sooner, he could have started medication sooner, and whilst the medication doesn't cure dementia, it acts to sort of slow it down and eliminate the severity of it."
In the survey, more than a thousand families and carers of people living with dementia revealed that nearly half of them waited for more than six months for an accurate diagnosis after their first visit to a GP.
Michelle Dyson CB, of the Alzheimer's Society, says a diagnosis can really help families access support and plan for the future.
"Too many families spend months, and sometimes years, waiting for answers while their dementia progresses.
"It is like trying to plan a journey without knowing where you are going or when you will arrive.
"You would never accept someone being diagnosed with cancer and then left to work out the next steps on their own."
Dementia does not wait, and neither should diagnosis, she added.
Keith and Sue Andrews first met when they were 15, and they've been married for 57 years.
Sue's condition has deteriorated so much that she now lives in a home.
Keith says they had to wait almost a year for a diagnosis, which was difficult.
He says life became more maneagable, once they knew for sure.
"I won't say it's easy, but you know where you're going, and you know where you're heading and you feel a lot more confident in what you're doing.
"Because you know you're doing the right thing, but before that diagnosis, you don't know if you're doing the right thing or what to do even.
"And it's a horrible time, a horrible time."
Like Keith, 9 out of 10 families surveyed said that a formal diagnosis made at least one aspect of life easier.
That included understanding symptoms and behaviour, supporting the person living with dementia, accessing information or speaking to healthcare professionals.
A spokesperson for the Department of Health and Social Care said:
"This Government is determined to strengthen the support that is available both to individuals affected by dementia, and the family members who look after them.
"We are bringing forward the timetable for Baroness Casey's commission on reform of the social care system, and we are appointing a new dementia tsar to help lead our work in that area, as recommended by Baroness Casey."
"We are also implementing a new action plan for unpaid carers to ensure that they receive the support and recognition they deserve for the selfless work they do."
