People put off visiting their GP with symptoms of dementia due to fears that their lives "will be over", research suggests.
A poll for the Alzheimer's Society found 56% of 1,000 GPs had diagnosed people who had suffered with symptoms for many months, and sometimes more than a year.
In a separate poll, almost two-thirds (62%) of more than 2,000 people said a diagnosis of dementia would mean their life was over, while 45% expected they would be immediately forced to give up driving.
A quarter (24%) thought a dementia diagnosis would mean having to stop going out for a walk on their own, according to the survey carried out to mark Dementia Awareness Week.
Half (49%) said they would worry that people would think they were "mad", while 22% feared losing a partner or friends.
More than a third (37%) said they would put off seeing a GP about memory problems because they think dementia is just "part of the ageing process".
Jeremy Hughes, chief executive of the Alzheimer's Society, said: "Too many people are in the dark about dementia. Many feel that a dementia diagnosis means someone is immediately incapable of living a normal life, while myths and misunderstandings continue to contribute to the stigma and isolation that many people will feel.
"This Dementia Awareness Week, we want to reassure people that life doesn't end when dementia begins.
"We know that dementia is the most feared health condition of our time and there's no question that it can have a profound and devastating impact on people, their family and friends - but getting a timely diagnosis will enable people with dementia to live as well as possible."
Figures from the charity show 225,000 people will develop dementia this year - one person every three minutes.
Joy Watson, 57, from Eccles, was diagnosed with early onset dementia in 2014 after being told her symptoms amounted to depression.
She said: "When my GP finally told me I had Alzheimer's, after six years of battling with symptoms and not knowing what the cause was, I felt huge relief.
"For so long, I didn't know or understand what was wrong. All I needed was a diagnosis to be able to move forward with my life - and now I can."